A massive floor boss has crashed down from the upper floors and begun tearing apart the adventurers. Aiz has left for the surface, and it's up to Bell and his friends to defeat the monster. With their escape route cut off, it's do or die if they ever want to see the light of the sun again.

A massive floor boss falls from above and traps the adventurers. The only way out is up, and to get back home Bell will have to defeat it without Aiz's help.