As he's living out his amazing slime life, Rimuru decides to record his experiences in a diary... but there are so many, he doesn't know where to start. That's just how life in Tempest goes.

Peace has come at last following the battle against the Orc Lord. In the midst of the duties that keep him busy, Rimuru finds himself with a day off. But when he tries to enjoy the break, he can't even figure out what to do and just ends up bored. He heads into town with Gobta to eat some food from the street stalls as they walk around, but in the end, he only feels more motivated to work the fields.

Summer has come to Tempest. When he learns that summers here weren't always this hot, Rimuru begins to fear that the change was his fault. Shuna and Shion have their own unique way to keep cool, and Rimuru tries to think up some fun summer activities... but bug-catching turns into bug-hunting when the bug he's after turns out to be enormous, and a game of shooting water pistols gets out of hand when Rimuru himself becomes a water cannon. With everything on a completely different scale in Jura, every activity he tries turns into pure chaos! And Rimuru has no idea that he himself is the ideal cold pack...

Extreme summer heat is ravaging Tempest. Rimuru and crew visit a lake they've been told lies beyond the forest, and they change into swimsuits to start having fun... but Shion and Shuna seem dissatisfied with Rimuru's swimsuit. Veldora watches the gang from inside Rimuru's body as he plays a game of shogi with Ifrit. As the Storm Dragon, one who has never experienced swimsuits or water play, he struggles to understand what all the excitement is about...

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...