Ou to Kemono - Se Inochi no Chigiriri

Xiezhi, a divine beast protecting the Kingdom of Twilight, was feared as the Grim Reaper, as kings who made contracts with him met their demise one after another. Xiezhi, who had closed himself off and refused to make new contracts, meets Jiyun, the son of the last king who accepted him. Seeing Jiyun's loneliness and relating it to his own doubts about his existence, Xiezhi proposes that Jiyun make a contract with him.