After defeating Clayman at Walpurgis, Rimuru officially became a Demon Lord and a member of Octagram. Meanwhile Diablo awaits Rimuru's return in Tempest, and is anxious to learn about his master's activities as soon as possible. A look back at Walpurgis.

Yuuki is saddened by the death of Clayman, and Luminus is saddened by the death of Roy. Steeped in sadness, and having lost their friends, they seek their next move against Rimuru, who has grown in power and become a true Demon Lord.