Wow, I'm on a roll. Started and completed this today. Another contest entry for IMAGINE, this time the theme is "Fusion with your demon partner" (Again, mind out of the gutter!).
I think there would be an upset in the cosmos if I used someone OTHER than Oni for this entry. He's been my main partner in the game since level 28; I'm level 90 now. No Megido-powered, anti-everything demon, he's just a regular Oni from Ueno. He's been rebirthed all to hell, though, so he packs a punch.