A powerful necromancer known as the Corpse God dies during a legendary battle, only to be reborn as Polka Shinoyama, a young boy in modern-day Tokyo. In the process of trying to adapt to his new physical body, he gets targeted by various groups that deal with the supernatural. Among them is Misaki Sakimiya, a high school girl who can see spirits and is out for his blood from the very moment they meet. Attempting to make sense of this situation where unknown parties want him dead, Polka eventually meets Takumi Kuruya, a contractor skilled in surveillance and hacking, and Lisa Kuraki, a crime boss operating out of Shinjuku. Alongside these—and other unexpected—allies, Polka braves danger to reveal the truth of his reincarnation and the fate awaiting the world he now lives in.

Far in the future, the lifeforms known as Gadoll suddenly arose as a threat to humanity. The last surviving humans on Earth confine themselves to the Tank, a lower district in the giant mobile fortress Deca-Dence. While the Gears who live on the upper floors are warriors who go out to fight as part of the Power, most Tankers are content to provide support from the backlines, butchering Gadoll meat and reinforcing defenses. Natsume is among those who would rather go to the front lines; undeterred by her prosthetic right arm, she seeks to join the small number of Tanker soldiers who join the Gears in combat. But despite her peers at the orphanage each receiving their work assignments, Natsume’s enlistment to the Power remains unapproved. In the meantime, she begins a job as a cleaner in an armor repair team led by the hard-nosed and apathetic Kaburagi, who seems to be more than he lets on. Though initially cold to his idealistic subordinate, he soon recognizes in her the potential to upset the status quo of the world. As Natsume’s new mentor, Kaburagi prepares her for the special and unique role as a game-changing bug in the system.

During a regular after-school grub crawl, gluttonous high schooler Hibiki Sakura is confronted about her ever-expanding waistline by her best friend, Ayaka Uehara. With her attempts at solitary exercise failing miserably, Hibiki decides to join the newly opened Silverman Gym. At her orientation, Hibiki runs into student council president and school idol Akemi Souryuuin. However, it soon turns out that Hibiki is in for a lot more than she bargained for. Not only is Silverman Gym full of world-renowned bodybuilders and athletes, but to make matters worse, Akemi turns out to be a total muscle fetishist! Grossed out by the scene unfolding before her eyes, Hibiki begins to leave, only to be stopped by trainer Naruzou Machio. Completely enthralled with her newfound Prince Charming, Hibiki signs up as a gym member. Now, as a result of her spur-of-the-moment decision, Hibiki must adapt to her new lifestyle.

Waking up to find herself in a parallel version of Fuyuki City, Illyasviel Illya von Einzbern is lost and alone. She discovers her home in ruins, with a massive crater lying in the center of her hometown. With snow falling in the middle of summer, confusion consumes the young elementary schooler, who has no knowledge of where her friends or her wand Ruby may be. Making it to the remains of her house, she is suddenly tackled by an amnesiac girl. Wearing a gym uniform as the icy temperature sets in, the mysterious girl has no idea of where she is or why she showed up. However, this stranger, known as Tanaka, apparently has information about the location of Rin Toosaka, Miyu Edelfelt, and the rest of Illya's missing friends. Fleeing from agents of the Ainsworth family⁠—those in control of this parallel realm—where will these two end up, and how will Illya restore the present back to the world she once knew?