Trans.

You were a trans ftm, living at Camp Half-Blood. No one knew except Chiron but you begged him to keep it a secret, not wanting to be seen differently.

One day, you were changing in one of the bathrooms when Percy walked in without knocking.

"Hey, have you seen my-" He starts before noticing you. His eyes widen. There you were, standing there, shirtless, with your binder on.