Overlord: Blood Genealogy (2018)

Taiga Washio, the eldest son of the mafia leader Taro Washio, is a primary school student. He is trained for succession as the next leader. On the other hands, Kiyoharu is the deadest assassin in the mafia. When the leader Taro was killed by the enemy, the inherited war between Taiga and Kiyoharu begins.