Dungeon ni Deai wo Motomeru no wa Machigatteiru Darou ka IV: Shin Shou Yakusai-hen

Bell and Ryu end up in the 37th floor, which is a Deep Floor. The rest of the party are at level 27, facing the level boss Amphisbaena. They have to defeat the level boss, in order to save Bell. At the same time, Bell and Ryu have to find a way to stay alive on a floor with strong monsters while having to avoid the Juggernaut. (Source: Anime News Network)