The volume opens with the party arriving at , a towering industrial marvel where the water isn't just for washing—it’s the lifeblood of the city’s magi-tech engines. Touya, Haru, and the others are invited to the "Grand Obsidian Basin," a legendary bath said to grant temporary invulnerability to anyone who can survive its intense heat.

Trapped in a high-pressure steam room, Touya and Haru finally have a "heart-to-heart" that isn't interrupted by a monster attack... until the bath duck familiar, Piyo, accidentally triggers a secret trapdoor. The Climax

Touya and his companions had survived demonic sieges and divine trials, but nothing prepared them for the of the Iron Kingdom. In this seventh leg of their journey, the legendary "Cleaning" magic faced its steepest challenge yet: a bathhouse built inside a dormant volcano. The Plot: Steam and Steel

The volume concludes with a massive battle against a that has nested in the primary boiler. Touya realizes that the dragon isn't evil—it’s just extremely itchy. Using a mountain-sized amount of "All-in-One Body Wash," Touya performs the largest exfoliation in the history of the world, turning the beast into a shiny, docile ally.