Throughout the series, Percy Jackson and Annabeth Chase have shown many romantic feelings for each other; mainly in The Last Olympian and The Battle of the Labyrinth, though Annabeth shows it more than Percy, and Percy thinks about it instead.
When Percy wakes up he describes Annabeth as a "pretty girl, her blond hair curled like a princess". During their quest, Annabeth and Percy both feel awkward at stepping into the Tunnel of Love. They eventually go in, which leads to Percy saving Annabeth from the spiders that are part of the trap designed by Hephaestus to catch Ares and Aphrodite.
Later, with the help of Ares, the three hop on a truck heading west and Annabeth and Percy talk about the possibility of war between the gods while Grover sleeps. They briefly talk about their personal backgrounds (mainly of their god parents), and Percy asks her that if the gods do go to war; would Poseidon and Athena be on opposite sides like they were during the Trojan War. Annabeth admits she doesn't know, but would fight alongside Percy regardless as they were friends, before asking if he had any more stupid questions.
When going into the Underworld in the boat, Annabeth takes hold of Percy's hand to make sure she's not the only one alive and Percy said he normally would've been embarrassed, but he wasn't at the time.
Annabeth admits at sixteen that she had a crush on Percy since the age of twelve.
Annabeth begins to show slight feelings for Percy (and vice-versa; though, more Percy is less than Annabeth- for now). Percy was shocked when he saw Annabeth with make-up on C.C.'s island and thought he would be tongue-tied if he weren't a guinea pig. She hugged him when he changed back to human, cried on his shoulder while hugging him underwater (after he saved her from the Sirens). At the end of the book, she kisses him on the cheek following their success at the chariot race.
Percy and Annabeth dance in the beginning after Percy was jokingly punched by Annabeth, after asking who he should dance with. While dancing, Percy was nervous and "tried to focus on little things- the streamers, the punch bowl- anything but the fact that Annabeth is taller than me, my hands are probably sweaty and gross, and I'm stepping on her toes". After slow-dancing with her, Percy found out that Annabeth almost became a Hunter at one point, and that the option is still open. Percy is terrified that Annabeth would leave him. When Percy meets Aphrodite, she makes Percy reveal aloud that the reason for going on the quest was mostly about Annabeth. Annabeth wanted to go back to holding the sky so Artemis could fight, but Percy took the weight. Later, while she seemed grateful to all of the people who rescued her, she expressed her gratitude mostly to Percy. At the end during the Olympian party Percy suggests they finish their dance and she smiles, takes his hand, and they dance. Percy hears a slow song and wonders what other music everyone else hears.
|“||She glared at me like she was about to punch me. Then she did something that surprised me more. She kissed me. 'Be careful, Seaweed Brain.' Then she put on her hat and vanished. I probably would've sat there for the rest of the day staring at the lava and trying to remember what my name was, but the sea demons jarred me back to reality.||”|
During breakfast one day, Annabeth broke the rules and sat at Percy's table (like really close to him) to talk about their upcoming quest, which Percy really liked. Before the quest, Annabeth and Percy hugged. Annabeth got extremely jealous and moody every time Percy mentioned Rachel Dare. When they found the Labyrinth, Annabeth held Percy's hands which to Percy if it was public, he would have been embarrassed, but it was dark and they were together. Then, when Percy walks into the Athena Cabin to talk to Annabeth, he asks her what the last part of the prophecy was about. In response, she tears up and holds out her hands, and Percy walks over and hugs her. They are later interrupted by Malcolm, and awkwardly say they were preparing for the quest. In Mt. St. Helens, when Percy risked his life so Annabeth could get to safety, she kissed him and disappeared, putting on her magic Yankees cap. She and the rest of camp presumed he was dead, as he was stuck on Ogygia for two weeks. When he returns, Annabeth hugs him fiercely until she realized she was making a scene. She was furious at Percy for being gone so long, and when she figures out where he has been marooned to (and had been with Atlas' daughter, Calypso), she gets even madder with extreme jealousy. When they return to Camp Half-Blood, and when Percy is about to go, their relationship is slightly shaky.
To Percy, Annabeth looked like beating him was the best thing she wanted to do. According to Beckendorf when girls look like that it means they like the boy. After Percy, Silena, and Annabeth manage to save Beckendorf from a swarm of Myrmekes (robot ants) during a game of Capture the Flag, Annabeth and Silena turn on them and take them as prisoners of war. As Annabeth leaves to finish the game, she tells Percy she will see him at the fireworks show, which is the most romantic event at camp. However, she doesn't wait for his answer and runs away before he could reply, leaving Percy to wonder if she just asked him to the event.
|“||You've been known to call Percy "Seaweed Brain" from time to time. What's his most annoying quality?||”|
–Interviewer, in The Demigod Files
During the interview section of The Demigod Files, Annabeth was asked what Percy's most annoying quality. She says that it is how he acts dumb and it annoys her. While ranting about this, she unintentionally points out his good qualities, including how courageous he is, how funny he is, and that he is good looking (which she warns the interviewer not to tell Percy she said that). She also says that Percy doesn't know how people are feeling, even when they are dropping hints and being blatant, but she claims she isn't talking about anyone in particular and that everyone thinks she is talking about her and Percy (it's obvious that this is what she is talking about).
As Percy and Annabeth are inspecting the cabins at camp and arrive at Athena's, Annabeth begins to say something about her feelings for Percy, but is interrupted by Annabeth's second-in-command Malcolm. Percy finds this awkward and nervous as the rules were that demigods of the opposite gender were not allowed to be in one cabin alone if they are not related and changes the subject. While Percy was bathing in the River Styx, he had to choose one thing to think of to keep him anchored to the mortal world. He imagined Annabeth pulling him out of a Camp Half-Blood lake, saying "Hold on, Seaweed Brain, you're not getting away from me that easily," causing the cord connected to his lower back to strengthen and eventually pull him out of the river.
During Camp Half Blood's war preparations, or during the war itself, every time a difficult task was at hand, Percy would volunteer either to protect Annabeth, or to ask for her help. When Percy was about to get stabbed at his one weak point during a battle (he would have died immediately), Annabeth intercepted the blow even though Percy never told her where his weak spot was. Percy immediately became very defensive of her, making sure no one touched her. Kronos found this interesting. Later, as Annabeth was healing, she and Percy were immersed in a conversation that was quickly escalating into a romantic moment, but Connor interrupted and stated that Grover had arrived.
On the way to Mount Olympus, they cross the dangerously crumbling bridge. Everyone gets to the other side safely except Annabeth. She almost falls, but Percy saves her with the help of his friends. As Percy pulls her back up, they realize that their arms around each other and awkwardly untangle themselves.
Soon, Kronos/Luke finally comes to Olympus and Annabeth, Percy, Thalia, and Grover are the only ones there to protect the ancient city. A statue falls over Thalia, and she urges them to go on. Grover gets knocked out almost immediately. Kronos strikes at Percy and paralyzes him. Then Kronos goes for Annabeth and mortally wounds her. Luke regains control of himself, and stabs himself to kill Kronos once and for all. As he lay dying, he asked Annabeth if she ever loved him. She replied that she thought of him like a brother, but never truly loved him at all.
Near the end, as Percy is being offered immortality and life in Olympus, Annabeth feels horrified that Percy would leave her, similar to the way Percy felt when she almost became a Hunter. He turns down the offer, primarily because of Annabeth, and she cries in relief. Back at camp, Annabeth holds a private birthday party for Percy, with a homemade cupcake. Percy confesses his vision in the River Styx. He tries to tell her how he feels about her, but Annabeth simply smiles at him, as if she was trying to hold in her laughter. Percy complains that she isn't making things easy for him, to which Annabeth replies by putting her arms around his neck and saying that she would never make things easy for him. She kisses him there and then, while Percy states that he felt like his brain was melting right through his body, and that he could stay like that forever.
However, the campers, lead by Clarisse La Rue, interrupt and pick them both up, but allow them to be close enough to hold hands. They dump Percy and Annabeth into the lake, expecting them to resurface. But because Percy is a son of Poseidon, he creates an air bubble around the two of them, not unlike the one in the Bay of The Sirens in The Sea of Monsters, and they share what Percy describes as "the best underwater kiss of all time". They officially start their relationship, and when Annabeth says she wants to be an architect to make something permanent, Percy says that they were "off to a great start." Grover remarks that he is still Percy's best friend and that nothing has changed - "except for Annabeth". Percy replies by saying that "That's different", to which Grover agrees. As they leave Camp Half-Blood for the year, as they race down the hill, Percy states; for the first time, he "didn't look back".
It is stated that Percy is Annabeth's boyfriend, showing they are in a relationship. Annabeth meets Jason, Leo, and Piper when she and Butch arrive to take them to camp but she really came because she was told Jason would know where Percy is. Also, she goes looking for Percy again the same day Jason, Piper, and Leo depart for their quest.
It is confirmed in the first chapter that besides Percy's own name and heritage as a demigod, Annabeth is the only aspect of his life that he can recall to any extent at that point. Not long after, Percy has a dream in which Annabeth, as well as Grover, appears telling him to "stay put". Percy has some internal conflict about leaving camp due to her warning, wanting desperately to see her, but ultimately leaves camp to complete the quest after making a promise to her that he would return. During the quest, Percy recognizes that though he wants very much to protect Camp Jupiter as well as his new friends Frank and Hazel, his drive for completing the mission relies heavily on Annabeth; he says his greatest fear is not the loss of his life, but that he might forget Annabeth's face as they get closer to Alaska. When returning to Camp Jupiter with his memory fully intact, Percy worries for his friends' safety at Camp Half-Blood. When Juno tells him that Annabeth would be an obstacle in the coming quest, Percy gets worried for her, as well as furious at Juno for taking eight months of his life with Annabeth and his other friends. As the Argo II finally arrives, Percy realizes Annabeth must be on the boat and thinks that, despite his lost time, it would be the greatest day of his life.
Throughout the book, Percy consistently refers to Annabeth as his girlfriend, even turning down blatant courtship from the Amazon Kinzie (as well as another insinuated courtship from Reyna) by saying he's already romantically involved. He also mentions many instances of past kissing, as well as stating that the two months he'd been dating Annabeth had been fantastic. Humorously, Percy mentions a down-side to dating the smartest girl at Camp Half-Blood: he actually learns things.
It is confirmed that they are dating. Percy forgets their one month anniversary. To make up for it, he makes a deal with Hermes. The deal is that if Percy and Annabeth complete a quest to retrieve Hermes' staff from the fire-breathing giant Cacus, the god will take them to Paris. At the end, Hermes ends up taking them to Paris for their one month anniversary.
Annabeth mentions that she had had a crush on him since she was 12, and that her feelings for him grew exponentially once he disappeared. Percy's love also grew exponentially to the point where he liked certain aspects of Camp Jupiter because he was thinking of their future. He mentions this to her towards the beginning of the book, and it is a major point of re-connection between the two.
There are many instances throughout the book where Annabeth is stuck thinking about the amount of pain she experienced during the 6 months that Percy was missing. Especially at the beginning, it seems as if her experiences during this time would end up harming their relationship, simply due to the level of hurt and loss that she experienced. While this does not entirely disappear through the middle and end of the book, it is clear by the end that their positive feelings for each other have overcome any previous pain that they have been through.
There are also moments throughout the book where it is evident that Percy and Annabeth are growing closer, and falling in love. At the beginning, Annabeth realizes that Reyna had made a move on Percy, and that he rejected Reyna for Annabeth. Annabeth promptly silently forgives her boyfriend for everything he's ever done wrong because of that. On the ship one night, Annabeth wakes Percy from his nightmare and takes him down to the ship's stables. She says she likes the stables for a reason, and once he looked around, Percy realized that she liked it because of a memory they both share. It reminds both of them of the time when they first actually talked on their first quest riding in the back of an animal transport truck.
Percy also mentions to Annabeth that back in New Rome, demigods could grow up and have families, indirectly implying that they may be able to do the same. Annabeth finds that to be very sweet, but says that they probably ruined any chance of cooperation with the Romans and it probably wasn't possible. Percy gets shy and tells her that he would think that to give him hope that he would be reunited with her. They stay down there, talking for a bit, before falling asleep in each other's arms. In the morning, Frank finds them, and to their humiliation, Coach Hedge grounds them both in front of the other passengers. Later in the book, after Percy rescuing Annabeth, Hazel, and Piper from Octavian and two others, Annabeth throws her arms around Percy and says, "I love you!", though this was probably said in the heat of the moment.
Whenever Annabeth or Percy gets in danger the other always is off to the rescue and is worried sick. After being apart for so long, a separation is almost unbearable. Percy finds himself wanting to make up for lost time, but also realizes that he can only imagine to a small extent what it must have been like for Annabeth, to endure for 8 months, not knowing where he was or if he was even alive. This mutual realization and subsequent sharing of the strength of their feelings for each other eventually leads to the promises that they make never to leave one another. This culminates in their final scene of the book, where Annabeth is about to be dragged into Tartarus by her entanglement in Arachne's webs. While they are both hanging off the edge of the chasm, with Percy holding on to her, they both realize that they are beyond the help of the other demigods. Percy demands that Nico promise to lead the others to the side of the Doors of Death which exists in the land of the living. Percy asserts to Annabeth that everything will be alright as long as they are together, and she understands the choice he is about to make. He lets go and they both fall into dark that leads to Tartarus. Nico later states that Percy is the most powerful demigod he has ever met, and if anyone were to survive Tartarus, it would be him.
There is a profoundly tragic element to their relationship, which appears in a more complex and troubling manner than the general personal tragedies of the first series of books. After all they had been through together in the first five books, they had finally overcome their own personal issues and reached a point where they could be happy together. In this new series, they can both barely comprehend the cruelty of their situation, in that they were separated when they had finally found an instance of peace together. Even in this book, they were hard put to understand the implications of their separation, but were eventually able to overcome the tragedy of their separation. Despite this, their hardships as a couple will undoubtedly reach a level that even they have never experienced before, as they will both have to struggle to make their way out of the darkest, most painful situation they have ever experienced - Tartarus itself. However, both of them seem to accept that it is because of being demigods.
While still falling in Tartarus, Annabeth tells Percy "I love you", thinking that if she dies, those should be her last words. Throughout the book, it is mentioned several times that Annabeth is deeply in love with Percy and that she cannot live without him. She also thinks about their future at Camp Jupiter, which Percy mentioned before, and she states that she would like to die peacefully, after spending a long life with Percy. Percy meanwhile, returns her feelings, and it is mentioned that he had nightmares of Annabeth's death, something which frightened him.
Percy cares for her a lot, but he constantly thinks of sacrificing his life to save her, whereas Annabeth wants Percy to be alive, so that she can live with him. Towards the end, Annabeth kisses him, saying that she would tell Percy what she had in her mind about their future, after defeating Gaea.
Jason first meets Piper on the Wilderness School bus, and once seeing that he was resting on Piper, he calls her "pretty," but he doesn't recognize her since they had never actually met at the time. Jason and Piper hold each other face-to-face when Jason saves Piper from falling down the Grand Canyon. He mentions that he couldn't pretend that he wasn't a little tempted to kiss her when they'd held each other like that. Jason mentions that he didn't want to leave her side when she was knocked out.
Piper developed feelings for Jason during the school year, but he wasn't actually there and it was all just a trick of the Mist. When Aphrodite claims Piper at camp, Jason calls her a "knockout" because she's so beautiful in his opinion. It is also revealed that Jason was extremely protective of her when she was knocked out due to the vision from Hera/Juno.
They bond over the course of the quest, wrapping their arms around each other for different reasons, and at the end of the book they meet at the basketball court. There they don't kiss, much to the dismay of the Aphrodite campers. Piper also tells Drew to back off from him because earlier in the book Drew was flirting with him.
Leo states that the two are now an official couple, and that Piper looks a lot happier. Piper also gives Jason a goodbye kiss in case she never sees him again.
Annabeth addresses Jason as Piper's boyfriend, which shows that the two have officially started a romantic relationship. Jason reveals to Piper that he prefers her over Reyna on the Argo II. They kiss multiple times throughout the book. Piper tells Jason she loves him while they are drowning, even though they both survive.
Juniper is completely supportive of Grover, despite what the Council of Cloven Elders think about him.
Juniper is shown to be quite worried about Grover's disappearance. At the end of the book, she tackles and hugs Grover fiercely when he is made a Lord of the Wild.
Percy finds Clarisse in the Big House basement trying to comfort Chris who has been driven mad. It is shown that she really cares for him. Near the end of the book, Dionysus cured Chris of his insanity. He and Clarisse were holding hands at the camp fire.
Chris and Clarisse both appear in the book. Clarisse refuses to fight in the war, although Chris tried to convince her otherwise. They both show up when the Ares Cabin leave camp and Clarisse fights the drakon after Silena Beauregard is killed. Chris goes after her to keep an eye on her.
When Percy, Annabeth, and Silena have to work together to rescue Beckendorf from the Myrmekes, Silena is extremely worried. Both of them have evident feelings for each other, Beckendorf getting tongue tied when Silena just walks past, and Silena was upset and angry at Annabeth when they didn't go to rescue Beckendorf right away. Beckendorf eventually asks Silena to go to the Fireworks with him.
Silena gets very depressed when she hears about Beckendorf's death. She also feels guilt for being a spy for Kronos. She says she wanted to quit but Luke blackmailed her, and also told her that Beckendorf would not be hurt. After Silena is killed by the drakon's poison, her soul goes to Elysium, where Beckendorf is waiting for her.
Rachel first meets Percy at Hoover Dam. She startles him, he swings a sword at her (which passes through her due to her being a mortal), she thinks he's crazy, but no romantic feelings are shown.
Percy has had thoughts about Rachel wondering who she is. Rachel meets Percy again at Goode High School and seems to be more interested in him.
Rachel kisses Percy when he leaves for a battle, but he is confused, because he also has strong feelings for Annabeth. Percy never really reaches a decision about what he feels for Rachel. Prior to her becoming an Oracle, Rachel had feelings for Percy (which offended Annabeth), but the "relationship" ended after Rachel decided that she wanted to be the Oracle. They still remain good friends.
Jason remembers Reyna after finishing his quest and her memory makes him rethink about his relationship with Piper.
|“||You say Jason is aboard...I hope that's true. I've missed him.||”|
–Reyna talking to Percy
It is revealed that Reyna believed that in time, Jason could have become her romantic partner, due to their partnership as praetors. However, he was taken away by Juno before a romantic relationship could begin.
Jason says that they were never a couple, and that he never thought of her that way, although it is very obvious she thought that way of him as this is shown in her moment of hurt when Jason asks to show Piper around Camp Jupiter.
|“||He couldn't read her expression. He was afraid he'd finally done something so weird that she'd never want to be around him again. Then she kissed him- a real kiss on the lips, much better than the kind of kiss she'd given Percy on the airplane.||”|
–Frank after defeating Alcyoneus
Frank and Hazel were best friends in Camp Jupiter. Frank mentions he likes Hazel a lot, but isn't sure she feels the same way and is afraid of telling her. Hazel on the other hand does like him, but because everyone at Camp Jupiter says they should be together (as they are part of the worst cohort), she is reluctant to tell him her true feelings. During their quest, Frank is very protective of Hazel and tries to cheer her up when she is feeling down. When Hazel feels that she should be dead and is just like the other undead beings that Gaea revived, Frank strongly disagrees and shouts that she is a good person.
Hazel in turn makes a strong connection with Frank when she brings him into one of her flashbacks. While Hazel relives her death and eventual sentence at the Judgment Pavilion, Frank watches as she gives up her place in Elysium so her mother wouldn't go to the Fields of Punishment. During this time, Frank hands her the burned stick that was connected to his life and asked her to take care of it for him.
Later, when Hazel rescues Frank from the Amazons, Frank says, "You, Hazel Levesque, are entirely freaking incredible," and Hazel thinks that she would just kiss him right there, but they are to busy running from the Amazons. Later, when they reach Grandma Zhang's home, Hazel makes Frank breakfast and gives him clean clothes. Frank's grandmother thinks Hazel is Frank's girlfriend. When Frank says they aren't, his grandmother tells him he shouldn't let her get away, as he needs a strong female in his life. After they defeat the giant Alcyoneus in Canada, Hazel kisses him. After that they seem to develop a romantic relationship, although it's not announced officially. Officially, they are confirmed to be dating The Mark of Athena.
Once Hazel meets Leo, their relationship gets a bit of a shaky start. For example, Hazel shows Leo a bit of her past in order to help him understand why she acts strange around him and help to understand their connection. In order to enter a flashback together, Hazel and Leo need to hold hands. When they exit their flashback, Frank sees them holding hands and looking into the each other's eyes (thanks to Coach Hedge's shouting). This causes Frank's jealousy to spike as he does not understand the situation and had been threatened by Leo ever since they first met. This eventually leads to Hazel and Frank having an argument. However, despite their relationship being a bit rocky, they are still very close and depend on each other.
Gleeson Hedge and Mellie
When getting information from Aeolus, Mellie seems attracted to Coach Hedge and he feels the same way. He even states that she was the kind of nature spirit that he could raise a bunch of baby goats with. Mellie also is impressed with his acts of bravery (even if he causes more trouble) and claims that he is very "goatly," a kind of compliment. After Mellie helps the group escape, she gets a job with Hedge to work for Piper's father as his assistant. They begin a relationship afterward. During Piper's talk with her dad, Mellie kisses Coach Hedge on the cheek.
Hedge has secretly been contacting Mellie throughout his time on the Argo II heading towards Greece. Hedge tells Frank that Mellie is pregnant and that they married in May just before leaving on the Argo II. He is worried about her because she is at Camp Half-Blood and the Romans are closer to the Camp and about to start a war, and she can't disappear. It is hinted that he may be a father now.
|“||Ella is not strong, Cyclopes are strong. Tyson found Ella. Tyson took care of Ella.||”|
–Ella talking to Percy
When Tyson and Ella arrive at Camp Jupiter after Percy calls them, Ella tells Percy that Tyson protected her as she wasn't strong. She also blushes around him. Tyson blushes too and whispers (loudly) that he thinks she is pretty. Later, when Tyson is fighting the Earthborn, she flies around him giving information on their weak spots. After the battle they sat at the same table during the Feast of Fortuna.
Sammy and Hazel were friends in Hazel's first life. However, she refers to Sammy as her old boyfriend when thinking about him. On Hazel's thirteenth birthday, Sammy sneaked her into the white only country club he worked at and the two went horse-back riding. They stopped and split a cupcake Sammy had brought, but it was a bit smashed from the ride, though they ate it anyway. Afterwards Sammy said good-bye to Hazel and kissed her on her cheek. She moved to Alaska later that day and Sammy never saw her again. Sammy eventually got married and moved to Texas, but died of a heart attack in the 1960s (later proven false). If Gaea hadn't convinced Hazel's mother to move, the two would have married (as seen in a vision Gaea showed her). Later when watching a video of Leo requesting a safe landing, Hazel sees Leo who looks exactly like Sammy. Percy, however, convinces her that this is impossible as Sammy would be much older and that the boy's name was Leo, not Sammy.
While having another of her flashbacks, this time with Leo, Hazel shows Leo how Sammy was when he was alive. During the flashback, Sammy protects Hazel from a bully and Leo can instantly tell how much Hazel likes him. The vision then changes to a moment from Leo's past, with Sammy meeting his great-grandson (Leo himself). In the vision, Sammy apologizes to Hazel as he had sold one of her diamonds so he could move to Texas and start his own business. He never forgot about Hazel and feels regret that he wouldn't be there for Hazel when she needed him. Sammy asks Leo to watch out for her instead, acting as his stunt double. During this vision, Hazel tries to tell him it wasn't his fault that she disappeared, but it is in vain.
It was hinted that the two might have had a romantic relationship before Thalia's last stand at Half-Blood hill. When Thalia first met the hunters, she declined their offer to join the hunt because of Luke. However, Thalia gets over her feelings for Luke when she is awakened and discovers his betrayal against the gods. Thalia defeats Luke on Mt. Othrys, and later joins the Hunters of Artemis, eliminating any last chances of a relationship.
There are hints throughout short story that Luke had liked Thalia, and that Thalia had had somewhat similar feelings for him as well. At one point, Thalia kissed him on the cheek and in turn, Luke was very protective of her. When Thalia told him that he was the best, Luke says it warmed him up like a cup of hot chocolate. He also says that he "should pick a partner next time that he didn't like so much."
Calypso and Percy Jackson
Percy gets washed up on the island Ogygia. Calypso nurses him back to health. Percy asks her why she pulls away when they're having a good time. Calypso tells him about her curse. When Percy has to leave, Calypso understands and lets him use a magical raft. Calypso gives Percy a clip of moonlace as a goodbye gift. Percy remarks her as 'his biggest what if'.
Calypso seems to still have romantic feelings for Percy. But she was angered that his promise wasn't made true by the Olympians after the Battle of Manhattan. Gaea offers Calypso that free her from her prison and raise Percy from Tartarus so that she could be with him. Unknowingly to Percy, Calypso had cursed his 'loved one', Annabeth, with the curse of despair, which was what she felt when Percy left her island. This is shown when both Percy and Annabeth encountered the arai in Tartarus.
When Reyna and Percy first meet, she develops feelings for him and asks to make him her co-praetor, claiming it will draw them closer as friends. Percy sees this as her way of flirting, and tells her that he already has a girlfriend. Later, when Reyna sees her sister Hylla, she glances at Percy and he states her eyes seem to be saying "I could hug you right now."
When Annabeth arrived, Reyna felt very jealous. Annabeth believes that Reyna must like Percy. Annabeth is also suspicious that the reason Reyna is jealous is because she tried to flirt with Percy and he rejected her.
Calypso and Leo Valdez
Khione sends Leo flying into Ogygia, where he is met by Calypso. While at first Leo doesn't like her, and vice versa, they gradually begin to grow closer, although claiming that they hate each other. When Leo is about to leave, she kisses him, saying that "that never happened." As Leo leaves, he swears on River Styx that he will come back for her.
When Piper, Jason, Hazel, Frank, and Coach Hedge find Leo, they are all feel down because Leo had lost his sense of humor. Jason realizes that Leo is heartsick over someone. When Frank mentions Calypso, who they do not know about yet, and Coach Hedge (being his normal self) jumps to a conclusion on killing her, Leo snaps.
Luke and Thalia run into seven year old Annabeth after their encounter with Hal. Luke gives her a knife, the knife that Annabeth always had until she lost it in The House of Hades. As Annabeth got older, her feelings grew for Luke.