Annabeth Chase
In The Last Olympian, after the defeat of Kronos and the saving of Luke's soul, the romantic relationship between Percy and Annabeth is solidified. Annabeth also states Percy looks 'cute when he's worried' when he first checks on her after she took a knife that was meant for him. Annabeth tells Luke as he dies that she always saw him as a brother, but never loved him. Later, she and Percy share their second kiss after she tells him that she will never, ever make things easy for him. He describes it as if his brain felt it was melting through his body. But nosy campers snoop on this and throw them into the camp lake. Then comes a third kiss underwater in an air bubble made by Percy. They are together at the end of the series. It is hinted that they might be married one day in the future, as Annabeth said she wanted "to build something permanent," and Percy states that maybe they were "getting a good start together.”