Yuuki asks Rimuru to investigate the Kingdom of Coleus, where a battle for succession has pitted the kingdom's two princes against each other. Rimuru launches a covert operation to sneak into Coleus and find out what's driving this conflict.

Aslan visits Rimuru to thank him for saving his sister, Zenobia. They discuss her illness and Souther's behavior, and begin to suspect that the court physician, Gustav, is behind both. Rimuru dons yet another disguise to investigate further.

Rimuru confirms that it was Gustav who cursed Zenobia with illness. It turns out he and his accomplice, Carl, are Archdemons plotting to manifest their god using Zenobia as a vessel. Can Rimuru stop them before the Kingdom of Coleus is lost?