A long-running conspiracy is swirling over a mysterious power wielded by the Queen in Raja, a small country west of Tempest. When a slime who evolved into a Demon Lord named Rimuru Tempest crosses paths with Hiiro, a survivor of the Ogre race, an incredible adventure packed with new characters begins. The power of bonds will be put to the test!

Toru Kamiya performs a false confession of love to stop his classmates' bullying. The story begins when Maori Hino, a girl in his class (whom Toru has made the false confession to) gives him three strange conditions for going out with him: "Not to talk to her until after school", "To keep communication brief", and "Not to fall in love with each other". Gradually, the promise of "Not to fall in love" falls apart, and Toru finally cannot hold back his feelings and confesses his love to Maori. However, Maori confesses to him that she has anterograde amnesia, which causes her to lose her memory in a day. Her memories and experiences are reset every day, and she writes down the day's events in a diary and wakes up early in the morning to review them in order to keep her memory alive. Toru is devoted to bringing her as many happy days as possible.

Miyu and Shuya are high school students. They have dated for 2 years. Miyu and Shuya have a promise that no matter what, they will watch a movie together on the first day of each new month. When Miyu and Shuya are on their way to the movie theater, Shuya suddenly cancels their date. Shuya seems like he is hiding something and he acts nervous. Later, Miyu goes to the place where she is supposed to meet Shuya, but she witnesses Shuya getting into a car accident. She panics, but when she wakes up she finds herself on the morning of the accident. Miyu keeps waking up on the day when Shuya got into an accident.