A nameless sword wakes up to discover he has been reincarnated from his former life as a human. With his power of telekinesis, he moves around this new world, acquiring several skills and abilities. When the sword comes upon a forest filled with monsters, he meets a young girl fleeing from a beast. Grabbing the sword, the girl easily defeats the monster. After introducing herself as Fran, she names the sword "Shishou" and officially becomes his wielder. The two set out to become adventurers, but unfortunately for Fran, she is a member of the Black Cat Tribe—a Beastkin group with a bad reputation. No member of this tribe has ever evolved into a mightier beast, but Fran plans to be the first and achieve her parents' dream. As Shishou promises to remain her sword until she attains her goal, they form an unstoppable partnership of impressive strength.

When aliens known as the Oni threaten to invade the Earth, they promise to leave under one condition—a randomly-chosen human must win a one-on-one game of tag against Lum, the beautiful daughter of the Oni leader. The "lucky" person selected happens to be the lustful and unlucky high schooler Ataru Moroboshi. Given 10 days to attempt to grab Lum's horns, Ataru realizes how impossible the challenge is as he is faced with Lum's extraterrestrial powers. Motivated by a promise of marriage from his childhood friend Shinobu Miyake, Ataru manages to catch Lum off guard. He mistakenly grabs hold of her bikini top first, but he eventually achieves his true goal. Although the game is over, Lum misunderstands that she is the one whom Ataru wants to marry, and she decides to move in with him. The poor student constantly tries to shake off the clingy Lum while doing his best to reconcile with his desired fiancée. After Ataru's heroic feat results in such a disastrous outcome, it is questionable whether luck will ever be on his side.

Following their heroic efforts at Walter Park, the students of the misfit class return to Babyls Demon School after their summer vacation. What awaits them is not only adoration and admiration but also the shocking revelation that, in order to stay in the luxurious Royal One classroom, the entire class must be promoted to Dalet rank before entering the second year. As the Harvest and Music Festivals are right around the corner, there seem to be ample opportunities to rank up. Doing so will not be simple, however, as no class thus far has managed to accomplish such a feat. Hoping to give the misfit class a chance to achieve the improbable, the school appoints special tutors to aid in confronting the challenges that lie ahead. With his sights set beyond Dalet, Iruma Suzuki decides to take strides toward the goal of ranking up, starting with gaining acknowledgement from his special tutor: the short-tempered and selfish Bachiko Barbatos.

After seeing enough death and tragedy, the immortal Fushi secludes himself on an island, defending himself from enemy Nokkers. However, instead of attacking Fushi in isolation, Nokkers begin targeting the settlements outside of his reach in hopes of luring him out. Soon, a group known as the Guardians—led by Hisame, the descendant of the deceased warrior Hayase—finds Fushi. Inspired by how Fushi protected Janada Island from the Nokkers years ago, the Guardians have grown a considerable following and are recognized throughout the world. Initially reluctant, Fushi allows the Guardians to accompany him to the site of the Nokkers' recent attack. In their village, Fushi meets a few valuable allies, both new and old. But as the conflict with the Nokkers only leads to more loss, Fushi must find the inner strength to face his inevitable sorrow.