I Became a Yakuza in Another World: My Peaceful Slow Life Will Have to Wait

Crow, a boy reincarnated into a fantasy world, one day finds Resina, the daughter of a yakuza boss, collapsed on the street. After his devoted nursing of her, she develops an intense obsession with him. This is the heroic tale of a boy who dreams of peace but unwillingly rises to become the “strongest yakuza boss in history.” — Description from novelcodex.org