My Uncle the Avenger
After the Giant War, you'd think Percy Jackson would be the most popular demigod around. Not accused of murder and shunned from the world of mythology, only trusted by Annabeth, Tyson and Grover. Scared and alone, he flees from Camp Half-Blood.
After fighting the Chitauri, all Tony Stark wants is peace. But one day while taking a peaceful stroll through Central Park, he comes across a certain aggravating teen, whom which he has a... say, 'disagreement' with. Leaving with a sour taste in his mouth, Tony can't shake Percy Jackson from his mind.
When these two so called 'enemies' meet, a secret is unleashed that surprises the both of them.
Percy Jackson has a mortal uncle.
That just so happens to be an avenger.