Caleo

Caleo is the het ship between Calypso and Leo Valdez from The Heroes of Olympus fandom.

Canon
Leo falls onto Calypso's island about halfway through The House of Hades, breaking her dining table in the process. Unlike all other heroes who came to Ogygia, Calypso does not fall in love with Leo immediately, nor Leo to her. But throughout Leo's time on the island, he starts to fall in love with her; Calypso starts to feel the same way, and begins acting nicer and not closing him out. When they are building the boat to get Leo off the island, a raft comes. This particular raft only appears when Calypso falls in love. Before Leo goes, Calypso kisses him, and he swears to come back to her. "I'm coming back, Calypso. I swear it on the River Styx."

In The Blood of Olympus, Leo dies and then comes back to life. He returns for Calypso on his dragon Festus. Thus, he fulfills the third line of the Prophecy of Seven: "An oath to keep with a final breath". The oath was Leo's promise on the River Styx to return to her, making him the first man to ever visit Ogygia twice. She hugs him and they "ride off into the unknown".

At the end of The Hidden Oracle, Leo comes back with Calypso, and they are enlisted to help Apollo on his quest. Then, in the next book, Leo and Calypso go to Indiana with Apollo and go to the way station house. Leo must go to Camp Jupiter, but once again promises to return and go to high school with her.

Fanon
This ship is relatively popular in the fandom. However, there are not many fanfiction centered around it, as it is usually a background ship.

Fandom
AO3

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Trivia

 * Thalia Grace was Leo's first love interest, and she is the only one who is at least partially human. The love in question was one-sided on Leo's part, though.
 * Calypso is the first out of four love interests to genuinely have any real romantic interest in him.
 * Leo is the only man who has ever reciprocated Calypso's affections and actually wanted a relationship with her.