Rimuru is building a dungeon in preparation for the upcoming festival. It will feature treasure chests containing weapons made by Kurobe, and Veldora will inhabit the deepest floor as the final boss. Then Milim suddenly shows up with a suggestion...

Cast: Miho Okasaki, Megumi Toyoguchi, Tomoaki Maeno, Makoto Furukawa, Sayaka Senbongi, Mao Ichimichi, Takuya Eguchi, Hochu Otsuka, Kanehira Yamamoto, Asuna Tomari, Chikahiro Kobayashi, Taro Yamaguchi