Thanks to the Fruit of Evolution, Seiichi Hiiragi's amazing new life in another world allows him to meet dependable allies and create formidable spells. His abilities catch the attention of Barnabus Ablitt, the principal of the Barbador Academy of Magic, who invites Seiichi to become a teacher at the institution. Coincidentally, Seiichi's classmates from Earth are enrolled there, which will lead to an awkward reunion if he is to meet them. Behind the scenes, however, an enigmatic cult called The Great Devil Order devises a sinister scheme to resurrect their deity and sacrifice the students of Barbador to hasten the process. As Seiichi's power is second to none, it is up to him to protect not only his friends but also the entire world from the looming darkness.

While exploring a labyrinth, Rentt Faina, an adventurer with lots of experience but little to show for it, is killed by a dragon upon discovering its lair. Shockingly, he wakes up to find himself turned into a skeleton, the lowest class of undead monsters. As Rentt fights against the other monsters of the labyrinth, he discovers that slaying them gains him experience towards higher stages of undead evolution—even ones with flesh! With this revelation in hand, Rentt obtains a new objective in his undeath: keep evolving in the hope of eventually becoming a vampire, the highest form of undead that is nearly indistinguishable from human beings. Despite being forced to hide his past identity and monstrous nature under an unremovable mask, Rentt manages to return to a semblance of his former life. Granted shelter by Lorraine Vivier, an elite researcher and retired adventurer, Rentt assumes her surname and starts over from scratch as a rookie. Determined to pursue his childhood dream and become a mithril-class adventurer, Rentt must be cautious not to disclose his new bodily circumstances, lest the adventurers’ guild seek to exterminate the monster he has become.

Losing their war against Heaven's angel army, the demons of Hell are on the cusp of collapse. As a last ditch attempt to turn the tides of the war, the demons send Akutsu Masatora to the mortal plane on Earth to save their homeland from the angels. Disguising himself as a high school student, Akutsu seeks to recruit someone with the capability to lead the demons to victory. Akutsu does not have to look far: among his classmates is the magnificent Lily Amane, a transfer student who seems like the perfect candidate for Akutsu's plans. But as luck would have it, Lily is one of the very angels that Akutsu is meant to be fighting against, and his attempt to recruit her might end up being the biggest blunder in the failing war. Worse yet, Akutsu may fall in love with his own worst enemy.

Rishe Irmgard Weitzner finds herself in a familiar situation: her fiancé is publicly breaking off their engagement, and her ducal family is about to disown her in shame. However, Rishe is not distraught; she has already had six chances to rebuild her life and chase a different passion each time. But she would always get swept up in a war and die, so now she wishes for her seventh reincarnation to be easygoing and uneventful. What Rishe does not take into account is the presence of Arnold Hein, the crown prince of the Galkhein Kingdom. He is destined to usurp the throne and become a tyrant who starts a large-scale invasion of neighboring countries. To make their encounter worse, Arnold is the one who killed Rishe in her previous life. That is why it is all the more shocking when he proposes to Rishe on the spot. In pursuit of her desired life, Rishe must consider accepting Arnold's proposal and discover the reasons behind his brutal actions to stop the war from ever happening.