So this is a concept I came up with a while ago but could never really bring myself to write more than 4 to 5 chapters for (that's right there's more written just never uploaded) but I did have a lot of of set up figured out.
First I made him a mutant for a couple reasons, 1. To fit his powers and apperance, I took inspiration from Nightcrawler basically just being a being of another dimension as his mutant ability and ran with it, I even created a backstory for the dimension from which his powers originate being that long ago it was for a time connected to earth before being disconnected by the sorcerer supreme of the time, the dimension in question being home to the Oni and the Origin for the myths, with that the reason Itto could control the earth would be that with the oni dimension there would be four tribes of Oni, avatar style and hapend to be a geographic Oni.
2. I made him a mutant to give some natural conflict as I didn't want the story to be a reincarnated story and I thought that it would also give me a chance to provide a neat background, that being a kid who was born in a still very rural part of America to immigrant parents who tried to protect their child before eventually being orphaned and chased off by the locals. With this I could build a natural hatred in the charcter for any sort of discrimination or injustice and build some heroic qualities by having him eventually saved and raised by a kind old lady.
I had him move to new York because, that's where everything seems to always go down and also to introduce him to many of the factions within new york.
I wanted him to eventually meet the ancient one while exploring the origin of mutant abilities with a mythos nerd friend in his school, this way he could visit this Oni dimension, gain some more power through training for any big bads I had in mind as well as gain a weapon through becoming the leader of the Geo Oni through a trial by combat which would simultaneously give him an army for endgame event.
I wanted him to mostly be a spider man like hero, focusing his efforts locally but occasionally helping with world ending threats. I also more recently had the thought of mutant discrimination rising after the blip and leading to an all out war event and the mutant having to create their own nation on an moving island made through Ittos geokenisis