Devouring Dimensions: Starting as a Marvel Nobody

Reborn as a lowly nobody in the Marvel Universe, he awakens the Devouring Evolution System, which lets him steal superpowers by killing and fuse them to make them stronger. To turn around his doomed fate, he devours heroes, villains, and creatures from other worlds with ruthless methods. In the end, he breaks through the dimensional barrier and invades the worlds of DC and Japanese anime, establishing a dark order.

[No beating around the bush, just get straight to it. No saintly protagonist. If that's not your thing, don't read.]