I was beaten up by the BOSS

The protagonist stumbled into a secret boss lair as a child, surrounded by death. The hidden boss discovered him and took him in, initially treating him like a plaything. Over time, their dynamic shifted—despite the boss’s ruthless nature, their bond began resembling something like family.

Titles:
Raised by the Boss
Growing Up Under the Boss
Beaten into Shape by the Boss
The Boss’s Unexpected Ward
Boss-Raised
Boss-Molded