Ragou

Rago is a legendary mononoke known as the Black Star of Doom, first encountered by Jiro Azuma after being forcibly unsealed by a group of hostile mononoke. Badly wounded, Rago was healed by Jiro — and when Jiro was killed protecting him, Rago repaid the favor by fusing with him, bringing him back to life. The fusion grants Jiro devastating combat power but costs him his humanity, and Rago later discovers a darker truth: sustaining that power means slowly consuming Jiro's own life force. Rago's release from his prison draws the attention of the Bureau of Espionage, pulling both him and Jiro into the organization's war against hostile mononoke, and eventually into a direct confrontation with Amagi, the mononoke who orchestrated his unsealing in the first place. Outwardly a small black cat with a star-shaped marking, Rago's true form is a colossal black panther.