Deep in the forest, far from any human contact, there lives a child named Ryouma Takebayashi. He engages in the rather strange hobby of keeping various types of slimes as pets. Furthermore, despite his young age, he has a sturdy physique and good compatibility for magic. All of this is because, having endured much hardship in his previous life, three gods grace Ryouma with a second chance to pursue one goal: savor the wonders of life. After three years of comfortable solitude pass by, Ryouma meets people that will change his current life forever. When he encounters and helps some soldiers tend to their wounded comrade, the group convinces him to accompany them to visit the nearby town's ducal family. Ryouma agrees and soon embarks on a journey to explore the vast world beyond his home.

Since reincarnating into a new world, Ryouma Takebayashi has used his god-given graces to tame countless slimes and employ them to improve the lives of everyone around him. With the astonishing success of his laundry shop, Bamboo Forest, he is finally ready to take on new frontiers and open a branch in the neighboring city of Lenaf. Abiding by his promise with his dearest friend, Eliaria Jamil, Ryouma makes every day count, whether learning new techniques, forming connections, or even discovering more species of slime.

Otaku siblings Tamotsu and Niwaka Denkigai are shopping in Akihabara when it is overrun by vampiric cosplaying monsters! These creatures, known as "Bugged Ones," can possess anyone they bite and soon they begin causing mayhem across the city. As Tamotsu finds himself at the mercy of one of these creatures, he is rescued by the mysterious baseball bat-wielding Matome Mayonaka. Together, they fight through several more encounters with the Bugged Ones, but before long, Tamotsu is fatally wounded protecting Matome. With no other choice, she revives him as a high level Bugged One—just like her! Tamotsu and Matome, along with excitable otaku cosplayer Arisa Ahokainen, make up the group "The Electric Mayonnaise" and they begin dispatching the Bugged Ones in the only way they know how: by ripping off their clothes and exposing them to sunlight!

Third-year high school student Jirou Yakuin is in love with his childhood friend and classmate, Shiori Sakurazaka. Thus, he hopes to be paired with her for the marriage practical: their school's practice of randomly selecting boy-girl pairs to live as pretend married couples while monitoring and rating them on how close they have gotten. Meanwhile, the lively Akari Watanabe wants to be assigned to her crush, the popular and good-looking Minami Tenjin. Much to their dismay, Jirou and Akari find out that not only have they been paired together, but so have Shiori and Minami! Determined to be with their crushes, Jirou and Akari strive to earn as many points as possible, as the top 10 pairs earn the right to switch their partners—so long as both couples agree.