Looking for fanfiction

Hi, I'm not sure if I should be posting in this subreddit. But here goes my question.

I was looking for something to read, a fanfic. But I can't find the kind of plot I'd like. Almost all the plots I see are set in the past, in the heroes' timelines and stuff like that.

But I’d like to see one where the summoned being is the main character. Like, he shows up in the War for the Holy Grail as one of the summons. I could be more specific, but for something that specific, I might as well write it myself, hahaha.

I just want to read something like that—does anyone have a recommendation?