Leorai

Leorai is the family ship between Leonardo and Karai from the Teenage Mutant Ninja Turtles fandom.

Teenage Mutant Ninja Turtles (2012)
Leonardo is the first of the Turtles that Karai meets. While she attacks and fights with him often, she never does him any serious harm and just enjoys sparring with a worthy opponent. Leonardo, in turn, was both confused by and attracted to Karai (as shown in the episode "New Girl in Town"). She is dangerous, but Leo believed that there was some good in her but she betrayed him. She seems to be deceitful and manipulative in The Alien Agenda, using Leo's feelings for her against him, especially in his time of need.

In Enemy of My Enemy, she returns, seeking information about the Kraang from the turtles. This time, instead of wanting to fight the turtles, she decides to make a truce with the turtles in order to defeat the Kraang ship. She goes against the Shredder's orders because she knows they'll all die if they don't set aside their differences and take down the ship. At first, the turtles, mainly Leo, are very skeptical of her and decline her REQUEST for a truce, but after she leads it away from the Shellraiser, they comply. Because Leo saved her and allowed her to speak to all of Turtles, Karai develops some friendship for him. However, because he and his brothers tried to attack her father, the truce was called off and her trust in him was left now uncertain. Now she's vengeful towards the turtles and is willing to do whatever it takes to take them down.

It was revealed in the Season 1 finale that Karai is Splinter's lost daughter, Miwa, who was raised by the Shredder. Leo seems more aggravated with Karai as she wants to hurt him and his loved ones more often, he tells her that her vendetta is with him not his family.

In Follow The Leader Splinter told Leo that Karai is his daughter. Near to the end of The Manhattan Project, Part 1, Leo told Karai that Splinter is her true father but she neglects it. In The Wrath of Tiger Claw, Karai was thinking about what Leo said about Splinter being her true father. When Karai finally realized that Splinter is her father, she betrayed Tiger Claw in trying to terminate the Turtles and Splinter, which caused Tiger Claw to take Karai BACK to Shredder to be locked in a cell.

In Vengeance is Mine, Leo and his brothers staged a rescue operation to get Karai from Shredder. It worked well and Karai was reunited with Splinter. When Leo and Michaelangelo was training, Michaelangelo threw one of his water balloons at Leo, which made Karai giggle. When Karai was planning on taking down Shredder, Leo wanted come along with her. Karai came CLOSE to Leo and temporarily blinded him with a smoke egg. Splinter, Leo and his brothers went to rescue Karai again. Leo was about to rescue Karai when all of sudden Shredder broke the chain that was holding Karai's cage, which caused her to fall into the mutagen. When she becomes a mutant, Leo appears to be one of the only people (aside from Splinter) that can help briefly restore Karai's mind by reminding her of who she is. In the episode Tale of the Yokai, the baby Karai met Leo, who had traveled back in time.

In season 4, Leo and Karai are obviously growing closer than in Season 3 and before.