Hephaestus has another project. As usual, everyone doubts it. But he swears it'll work. It's supposed to change the gender of anyone that irritates him for a day. Just for a day. Then it explodes, and everyone in Camp Halfblood and Camp Jupiter switches genders. Loved ones don't remember that Percy is supposed to be a boy or Piper is supposed to be a girl or what have you. Neither do the victims, for that matter. Even their parents think that these are their original genders.
Some swearing.
Names:
Percy Jackson = Perrie Jackson
Annabeth Chase = Andrew Chase
Jason Grace = Jessica Grace
Thalia Grace = Ted Grace
Piper McLean= Peter McLean
Leo Valdez= Leah Valdez
Hazel Levesque= Harry Levesque
Frank (Fai) Zhang= Fay Zhang
Nico Di Angelo= Nicole Di Angelo
Reyna ARA= Ryan ARA
Octavian= Olivia
Calypso (So we can have a variation of Caleo): Chase
Chiron does not change genders. Neither does Lupa, nor any Gods or Goddesses or Titans, etc. Yada Yada Yada. Go on! Read it!