Tsuki Hyouka's manga / #Anti-hero(3)

manga96.com/復讐を希う最強勇者は、闇の力で殲滅無双する-raw-free/

Got summoned to another world as a hero to defeat the demon king. Stayed there for 10 years, and finally killed the DK. But then, the "God" of this world appeared and told him he failed since he killed his comrades and that with great powers come great responsibilities blablabla. So he got sent back to his first day in this world.