Tucked in the mountains near the elite Kunugigaoka Middle School lies a small derelict building that houses the delinquents and dropouts of Class 3-E. Looked down upon by their peers, the students in this class appear to have little hope in advancing their academic careers. That is, until the national government tasks them with eliminating the greatest threat to their planet: their new teacher. Having already destroyed the moon, the octopus-like professor—dubbed Koro-sensei—has now threatened to destroy the Earth by March of the following year. In light of their mission, the students have found that killing him is easier said than done. Not only can Koro-sensei move at speeds of up to Mach 20, but he can also resist almost every earthly weapon. Ironically, he also proves to be one of the best teachers Class 3-E has ever had. Training the class to excel in both their studies as students and skills as assassins, Koro-sensei is confident that his students' ingenuity and indomitable will could return them to the main campus. Through trial and error, Nagisa Shiota, as well as the other students of Class 3-E, must figure out Koro-sensei's weaknesses—and fast, for the very fate of the world depends upon it.

The final hour of the popular virtual reality game Yggdrasil has come. However, Momonga, a powerful wizard and master of the dark guild Ainz Ooal Gown, decides to spend his last few moments in the game as the servers begin to shut down. To his surprise, despite the clock having struck midnight, Momonga is still fully conscious as his character and, moreover, the non-player characters appear to have developed personalities of their own! Confronted with this abnormal situation, Momonga commands his loyal servants to help him investigate and take control of this new world, with the hopes of figuring out what has caused this development and if there may be others in the same predicament.

Thirty-seven-year-old Satoru Mikami is a typical corporate worker, who is perfectly content with his monotonous lifestyle in Tokyo, other than failing to nail down a girlfriend even once throughout his life. In the midst of a casual encounter with his colleague, he falls victim to a random assailant on the streets and is stabbed. However, while succumbing to his injuries, a peculiar voice echoes in his mind, and recites a bunch of commands which the dying man cannot make sense of. When Satoru regains consciousness, he discovers that he has reincarnated as a goop of slime in an unfamiliar realm. In doing so, he acquires newfound skills—notably, the power to devour anything and mimic its appearance and abilities. He then stumbles upon the sealed Catastrophe-level monster Storm Dragon Veldora who had been sealed away for the past 300 years for devastating a town to ashes. Sympathetic to his predicament, Satoru befriends him, promising to assist in destroying the seal. In return, Veldora bestows upon him the name Rimuru Tempest to grant him divine protection. Now, liberated from the mundanities of his past life, Rimuru embarks on a fresh journey with a distinct goal in mind. As he grows accustomed to his new physique, his gooey antics ripple throughout the world, gradually altering his fate.

Hachiman Hikigaya is an apathetic high school student with narcissistic and semi-nihilistic tendencies. He firmly believes that joyful youth is nothing but a farce, and everyone who says otherwise is just lying to themselves. In a novel punishment for writing an essay mocking modern social relationships, Hachiman's teacher forces him to join the Volunteer Service Club, a club that aims to extend a helping hand to any student who seeks their support in achieving their goals. With the only other club member being the beautiful ice queen Yukino Yukinoshita, Hachiman finds himself on the front line of other people's problems—a place he never dreamed he would be. As Hachiman and Yukino use their wits to solve many students' problems, will Hachiman's rotten view of society prove to be a hindrance or a tool he can use to his advantage?