A character from the anime My hero Academia He isn't nice he just acts nice infront of other people. Kai's main usage of Overhaul outside of battle was obtaining DNA samples from Eri, which was realized by destroying her body, collecting some of her remains, and reassembling her back to life. Because Eri had access to a Rewind Quirk, Kai was able to experiment on her blood, transforming it into an ingredient for a special drug that could reverse a target's Quirk Factor, resulting in the target.