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.

Ittoki Sakuraba fails to understand why his mother, his uncle, and his childhood friend, Kousetsu, seem to take his security so seriously. Kousetsu constantly follows and observes him with no regard for his privacy, focusing only on keeping him safe every waking moment. But the consistent hounding starts making sense when an adorable second-year student at his high school, Satomi Tsubaki, asks Ittoki out on a date. Though initially innocent, Tsubaki's true intentions soon become apparent when Ittoki visits her house; she plans to assassinate him, and she is not alone. Surprisingly, the ones who come to his aid are his uncle and Kousetsu—donning their dark and deadly ninja attire. After Ittoki is escorted to safety, his mother reveals the truth: he is the 19th heir to a noble clan of ninjas known as the Iga, and the target of assassination by their rival clan, the Koga. In order to protect himself against this new threat, Ittoki must hone his skills at the only ninja academy remaining in Japan: the Kokuten Ninja Academy.

The race to obtain the lost Ainu gold is nearing its peak, as even more formidable ex-prisoners are set on keeping their tattooed skins intact. Saichi "The Immortal" Sugimoto and Asirpa can finally move forward together, but Asirpa's time with Kiroranke and Ogata Hyakunosuke has slightly altered her ambition and strengthened her determination. As their party leaves the Russian territory, they gain a peculiar follower. Meanwhile, Toshizou Hijikata's crew makes major moves to get invaluable skins, falling into the poisonous trap of a dangerous convict. Although each group possesses a strong advantage over the others, even First Lieutenant Tokushirou Tsurumi—the most powerful and ruthless contender—cannot advance without Asirpa's help. However, his ominous plans for when they will inevitably meet remain a mystery.

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.