Adui
I could do without all of the old baggage from his old world. Personally skip through stuff related to them. I'd personally have preferred if Mcs cheat was inate rather than random gift of his world. Like his unique skill. Also, that everyone has access to the system he does kind of takes away the awesomeness of him. Like, with enough time anyone could have done what has more or less. Just farm a ton of skills over and over and combine them while getting more stats from the beasts become able to fight. He was just the first one to kill the demon lords, but any of the people from his world could have perma killed one and gotten their skills.