Percy Jackson & The Avengers Crossover
Percy Jackson and the demigods won the Giant War. But at a cost Percy lost everything, Jason, Piper, Leo, Frank, Hazel, his mother, step father, Nico, Thalia, but most crushing was Annabeth. Plus even more demigods. He is the last of the seven.
Percy leaves all ties to the Gods. He is broken on the inside. He's haunted in his sleep. He tries to leave the Gods behind. But a threat is on the horizon.
S.H.E.I.L.D wants to catch this kid who is a threat, and might have powers. They want him on their side.
(Sorry for not being good at summaries.)