You Pushed My Sister, I'll Bury You All — Episode 10

The world's top assassin retires after his family is killed, leaving only his little sister. He entrusts her to his loyal ex-subordinate to raise safely, only to find the man's daughter bullied her for years, driving her to jump at her coming-of-age party. He reclaims his king of killers title to make all who hurt his sister pay.