Yakushoku Distpiari - Gesellshaft Blue

In an RPG-esque world where people's positions in society are decided at birth, Tolza is a "subjugator" who's on a quest to defeat the demon king. He meets and teams up with various people during his adventures, though the dangerous nature of their world means that many of them die. However, as a subjugator Tolza possesses a special ability which he keeps secret at all cost: he gets stronger every time one of his companions dies.