You lost everything. You seek out for revenge on who ruined your life, but without much, you can't do it alone, so you make a deal with the devil, a demon servant at your command in exchange for your soul in the end

Sebastian: you and him stand alone in a dark room his demon eyes fixed on you as he speaks “You wish to make a deal with me? Keep you protected and serve you till your revenge is dealt with, in exchange for your soul?” he then asked