Tensura nikki: Tensei shitara Slime datta ken

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...

In Great Sage's recollection, all seems to be smooth sailing for Tempest... but then the oldest of the Demon Lords, Milim Nava, arrives! Rimuru, as Milim's bestie, is appointed by the majority to be in charge of keeping an eye on her. With no knowledge of this, Milim explores Tempest and interacts more with the residents of the city of monsters... and Rigurd keeps track of all the damage she causes along the way in a report for Rimuru. "Rigurd... are you angry?"

It's autumn, and time for the harvest. Under the orders of Ririna, the Goblina in charge of the harvest, Gobta and his buddies get to work in the fields. Meanwhile, Shion and Milim make a contest out of digging up the sweet potatoes. With everyone working together, the harvest is over in practically no time, and Rimuru and the rest of the gang finally get to enjoy some delicious roasted sweet potatoes.

Most buildings in the monster city of Jura are made of wood, so in winter, a combination of dryness and heating mechanisms can lead to fires. So Rimuru starts up a good old-fashioned fire awareness campaign. Benimaru is selected as the mascot, but he seems troubled by the assignment... And in the midst of all these, the human Youm and his friends arrive in Tempest.

Winter has arrived in Tempest, and so much snow has fallen that its residents can't open their doors until it's shoveled away. But there are at least three like minds there who are finding it hard to resist their childlike urges to dive into the fresh snow: Rimuru, Milim, and Shion. Thus the work begins all around town to shovel Tempest out of the deep snow. Youm objects to being asked to help since he isn't even a citizen, but when he's given the choice between shoveling snow and training with Hakuro, he eagerly grabs the shovel and gets to work.

If you use Shadow Movement to sneak into houses and a pegasus team to pull the flying sleigh... yes, in this world, it's possible to become Santa Claus! But... the Christmas tradition doesn't even exist in this world. When Rimuru tries to explain it in detail to the people of Tempest, they end up summarizing it as a "party." The Christmas cake and presents are ready, and most importantly, Kaijin and the other Dwarves create gorgeous decorations that bring the Christmas mood to Tempest. On top of that, Eren and the children treat everyone in town with their heavenly singing.

Rimuru said he wanted to do a first shrine visit of the new year, so the citizens of Tempest built a shrine. But what deity is housed at this brand new shrine? Rimuru thought it must be Veldora, the guardian of the Forest of Jura, but everyone else says it's a shrine to Great Rimuru, so he ends up enshrined there... Thus their fun New Year's comes to an end, and Rimuru closes his diary. What will this new year bring? Tomorrow is sure to be packed with enough events to fill a new page...