Eugene and Sumire join the Martial Arts Club in exploring the Last Dungeon. Their combined strength makes the journey easy, but the sudden appearance of the Divine Beast Cerberus catches them by surprise. The Guard Dog of the Underworld normally only appears in a Deus Discipline, and no explorer in the past hundred years has ever been able to best it in battle. The members of the Martial Arts Club fall prey to Cerberus’s overwhelming strength, and Eugene realizes that if he wants to protect Sumire, he’ll need to form a contract with the Demon Queen Erinyes... no matter what she may ask for in return.