Re:Monster manga volume 12 features story by Kogitsune Kanekiru and art by Haruyoshi Kobayakawa.

Apo-Rou has taken his companions to the Flames Inferno Dragon Mountain, a God-Class Dungeon! In the very core of the volcano, he confronts the final boss-the Flame Dragon Empress. At the end of a fierce fight to the death where both use every attack in their arsenals, the time comes for a rank-up that could change the fate of Apo-Rou...and the world around him?!