Tokyo Revengers S01E18 - Open Fire

Back in present day, Ken tells Takemichi that Kazutora ends up killing Keisuke at the Bloody Halloween, the fight against Toman and Valhalla, and Manjiro ends up killing Kazutora. Because of that, Manjiro falls into darkness, and Toman is taken over by Valhalla, which leads to the evil organization that it currently is now, led by Kisaki. Takemichi goes back to the past with a new mission: to protect Keisuke so that this tragedy doesn't happen.