That Time I Got Reincarnated as a Slime: The Slime Diaries

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.

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.

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.

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.

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, and to strengthen friendships by telling others all about their own histories.