Rimuru decides to throw a summer festival resembling the ones held in Japan. The monsters have never experienced a summer festival, but when they hear that it's a party, they go all-in to prepare. All the monsters of Tempest work together and eventually come up with masks, paper lanterns, and even festival floats. On the day of the festival, everyone in the town enjoys piping hot takoyaki, cold shaved ice, yukata, and a Bon dance. In the end, they fill the skies with fireworks as the festival reaches its climax...

As the seasons turn, Rimuru plans a Bon Festival celebration. Each race has its own history, and the festival is a time to show gratitude and reaffirm their bonds among their own families and clans, and to strengthen friendships by telling others all about their own histories. And with this Bon Festival, Shizu-san returns to Tempest as a spirit...