After the war, Percy and Nico used their wishes to cut off from the Greek world. They join S.H.I.E.L.D. and are level 12 agents (there are only four level 12 agents them Natasha and Clint). They have been dating for a few years now. Director Fury asks them to help their fellow agents and avengers against the new threat. Disclaimer-I don't own Percy Jackson or Marvel. Uncle Rick and Stan Lee do respectively.