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.

As a corporate slave, Ryouta Satou experiences the worst forms of stress, overwork, and loneliness. Even after he is hospitalized due to exhaustion, his days of toil only become worse. Soon enough, the sheer fatigue catches up to him and kills him in his sleep. However, Ryouta is given a second chance at life: he wakes up in another world as a slime drop—much to the surprise of Emily Brown, the petite blonde girl who defeated said slime. Acquainting himself with the rules of this RPG-like world, Ryouta finds out that he will never grow past level 1. However, he also discovers that one of his skills is at the maximum level: the skill which determines the rarity of monster drops. This allows him to acquire not only items of the best quality, but also some that are unheard of. Ryouta sets out to make the most of his ability—meeting new friends, grinding through dungeons, and acquiring unique items along the way. Reveling in his new life seems to be the long-awaited and much-deserved reward for all the tribulations he had suffered.

The "Otherworld" is a vast and dangerous realm hidden from the knowledge of the common folk. It is also home to many creatures that threaten any human who dare visit it. To witness its desolate yet oddly absorbing environment, one must search for portals that could reside anywhere, from secret elevators to shrine entrances. After a fateful encounter with a horrendous Otherworld denizen, Sorawo Kamikoshi ponders whether to keep going or give up in life. Meanwhile, Toriko Nishina scours the Otherworld in hopes of finding her friend Satsuki, who she believes is lost somewhere within the realm. When the two cross paths, friendship blossoms. In order to acquire as much information about this obscure dimension, the two travel back and forth from the real world to the other. Sorawo and Toriko's bodies are soon influenced by the Otherworld, preparing them for the many horrors to come as both of them try to fulfill their goals.