There's Something Strange About My Chaldea

Overall, it's a crossover, though there'll be some real-world plot, too.

It should be a slow-burn story.

It starts in first person, then switches to third person later on.

Senior year of high school. Updates whenever I feel like it.

(The beginning... isn't very gripping, but I think the parts after [Starting with My Hero Academia... probably] aren't bad. Give it a quick follow. I won't disappoint you.)

A Certain Magical Index → My Hero Academia → Sword Art Online / Horizon