Transmigrating into the Hokage world during the Third Shinobi World War, Uchiha Qingyu isn't worried in the slightest, because he has Madara's template.
He can increase his fusion rate by killing enemies, and the battlefield becomes the perfect crucible for his growth.
At 30% fusion: I am a steadfast inheritor of the Will of Fire!
At 60% fusion: Shimura Danzō, born evil...
At 100% fusion: So you're the one called Otsutsuki!?
(PS: I'm no good at writing blurbs, so please read the story.)
(Also: This novel is all about saving those whose regrets never found resolution.)