Dark Guardian

Luce, the devil more infamously known as Lucifer, plans a wager with God over the pure-souled Elijah. But when Elijah finds out who he really is and asks him not to give up, Luce becomes his guardian instead — waiting for the day they'll strike a deal that could damn a soul... or change a devil forever.

(Source: Manta)

Note: Includes two extra chapters.