The Dark Fate (Nasuverse x Male Oc)

This is a story with a few twists, a boy name Ren who was the last survivor of the event of the Great Fire of Fuyuki, killing 500 people and destroying 134 buildings. He was saved by a man who will train him and be there as a father since Ren don't know his real parents. After a few years later he'll meet friends, girls that he will have as his love interest. He will participate in the event that other people will.

The Holy Grail