Yuuji Sano, a black company employee, is summoned to another world while finishing his work at home. His profession in the other world, a Monster Tamer, is considered a job that makes it difficult to become an adventurer. However, thanks to some slimes he met, which read several magical books, he gained magical powers and a second profession, Sage. Yuuji acquired overwhelming power, but is he conscious of his strength? Blindly becoming unparalleled and strongest in the world!

It happened suddenly: The dead began to rise and Japan was thrown into total chaos. As these monsters begin terrorizing a high school, Takashi Kimuro is forced to kill his best friend when he gets bitten and joins the ranks of the walking dead. Vowing to protect Rei Miyamoto, the girlfriend of the man he just executed, they narrowly escape their death trap of a school, only to be greeted with a society that has already fallen. Soon, Takashi and Rei band together with other students on a journey to find their family members and uncover what caused this overwhelming pandemic. Joining them is Saeko Busujima, the beautiful president of the Kendo Club; Kouta Hirano, an otaku with a fetish for firearms; Saya Takagi, the daughter of an influential politician; and Shizuka Marikawa, their hot school nurse. But will the combined strength of these individuals be enough to conquer this undead apocalypse? [Written by MAL Rewrite]

Since the death of his parents, Shinpei Ajiro had lived with the Kofune family and their two daughters—Mio and Ushio. Although he then left his home island to continue his education in Tokyo, Shinpei returns after Ushio tragically drowns during the attempted rescue of a little girl. During the funeral, his best friend informs him about bruises found around Ushio's neck, casting doubt over the cause of her death. Suspecting a murder has taken place, Shinpei reevaluates recent events, but strange incidents only continue to transpire. Disappearing people and other unexplainable occurrences lead Mio to recall an old folktale referring to entities called "Shadows," which may not be entirely fantasy. Supposedly, an encounter with one's Shadow foretells the person's impending demise. Facing the dark side of Hitogashima Island, Shinpei stands against his grim fate to fulfill Ushio's final will—to protect Mio.

When Demon Queen Echidna begins her invasion of the human realm, the people turn to the hero Leo Demonheart to protect them. Blessed with insurmountable power, Leo easily repels Echidna's army, thereby saving the world. But instead of gratitude or admiration, Leo is met with disdain and scorn from his fellow humans, who fear his overwhelming strength and believe that it may eventually cause humanity's demise. Banished from the kingdom he once called home, Leo wanders aimlessly throughout the land until, one day, he hears rumors of Echidna's efforts to rebuild her army. Hoping that demonkind might accept him as an ally, he returns to the demon queen's castle and offers Echidna his help. Naturally, Echidna immediately rejects him. Still, not all hope is lost, as Leo manages to convince Echidna's four generals to let him secretly work under their supervision. Donning the identity of a masked dark knight named Onyx, Leo solves the demon army's problems one by one—gradually improving the quality of life around the castle. Above all else, however, Leo wants to accomplish one goal: to learn why Echidna started the war in the first place.