The MC Dies and meets a ROB. (Random Omnipotent Being) And is allowed to reincarnate into an alternate world that highly resembles MARVEL (specifically the MCU). There are a few things different than the original for story purposes, but that is the primary source material. (powers that allow one to blow up the sun on a whim don't exist obviously)
He is given the 'Ultimate Villain System' A system that makes him the ultimate villain. Supposedly. You will have to read the story to find out.