Sixteen sentient races inhabit Disboard, a world overseen by Tet, the One True God. The lowest of the sixteen—Imanity—consists of humans, a race with no affinity for magic. In a place where everything is decided through simple games, humankind seems to have no way out of their predicament—but the arrival of two outsiders poses a change. On Earth, stepsiblings Sora and Shiro are two inseparable shut-ins who dominate various online games under the username Blank. While notorious on the internet, the pair believe that life is merely another dull game. However, after responding to a message from an unknown user, they are suddenly transported to Disboard. The mysterious sender turns out to be Tet, who informs them about the world's absolute rules. After Tet leaves, Sora and Shiro begin their search for more information and a place to stay, taking them to Elkia—Imanity's only remaining kingdom. There, the duo encounters Stephanie Dola, an emotional girl vying for the kingdom's sovereignty. In desperation, she attempts to regain her father's throne, but her foolhardiness makes her goal unachievable. Inspired by the girl's motivation and passion, Sora and Shiro decide to aid Stephanie in getting Elkia back on its feet, ultimately aiming to become the new rulers of the enigmatic realm.

After five years of harboring unspoken feelings, high-schooler Taiju Ooki is finally ready to confess his love to Yuzuriha Ogawa. Just when Taiju begins his confession however, a blinding green light strikes the Earth and petrifies mankind around the world—turning every single human into stone. Several millennia later, Taiju awakens to find the modern world completely nonexistent, as nature has flourished in the years humanity stood still. Among a stone world of statues, Taiju encounters one other living human: his science-loving friend Senkuu, who has been active for a few months. Taiju learns that Senkuu has developed a grand scheme—to launch the complete revival of civilization with science. Taiju's brawn and Senkuu's brains combine to forge a formidable partnership, and they soon uncover a method to revive those petrified. However, Senkuu's master plan is threatened when his ideologies are challenged by those who awaken. All the while, the reason for mankind's petrification remains unknown.

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.