The episode begins with Ryota and Celeste relaxing after a day of work. Celeste surprises Ryota with a cake and ice cream she prepared over the campfire, leading to a funny moment where Ryota is confused about how she managed to make ice cream over a campfire.

The next day, the Dungeonmaster appears, a powerful monster that only shows up every few months, causing everyone to panic. Ryota encounters Neptune from the Neptune Group, who explains to him that the cities of Secro and Hetero must assemble a joint team to defeat the Dungeonmaster. However, Hetero refuses to cooperate because they want the dungeon's ecology to change, which would restore the dungeon's ownership rights and benefit them. Ryota offers to defeat the Dungeonmaster himself, but Neptune explains that only a group of three adventurers with a status of A or higher is allowed to enter the dungeon.

Emily and Celeste decide to join Ryota. Inside, they encounter the Dungeonmaster, a unicorn, and engage in a fierce battle. The unicorn proves to be a powerful opponent, lowering their stats and forcing them to adapt their strategies. Celeste, who initially feels like a burden, plays a crucial role in the fight by using her Inferno spell to break through the unicorn's barrier, allowing Ryota and Emily to defeat it.

After the battle, Ryota and Emily gift Celeste the unicorn's horns, which allow her to use level 1 magic without restrictions. The trio returns to town, where they are celebrated as heroes for defeating the Dungeonmaster. Ryota invites Celeste to join them in forming a new party, "Ryota's Party," to which she enthusiastically agrees.