In the latter part of the fourth installment of Dungeon ni Deai wo Motomeru no wa Machigatteiru Darou ka, Bell and Ryu venture into the treacherous 37th floor, known as the Deep Floor. Meanwhile, their companions, stationed on the 27th level, confront the formidable boss, Amphisbaena, to secure Bell's safety. As the team strives to overcome this boss battle, Bell and Ryu must navigate the perilous environment teeming with powerful creatures, all while evading the menacing Juggernaut to ensure their survival.