Rikudou

リクドウ

Riku's childhood is a chain of violence: after his father's death, a former boxer turned yakuza teaches him a single punch, and that punch kills a drug dealer who comes after him. Marked as a killer and hunted by criminals who destroy everyone who tries to care for him, Riku returns to that same ex-boxer and asks to be made stronger, walking into a rundown gym and the brutal world of professional boxing.