Hit-Monkey (season 1)

After another mission, fleeing from his pursuers, an exhausted American hitman falls in a snowy Japanese forest. But the nameless killer does not die, a group of macaques finds him and rescues him. Strengthened and expecting an imminent reprisal, the killer begins to train hard, unaware that one of the monkeys is watching him closely, and then successfully learns all the techniques he has seen.