Alto Goldfilled, a diligent student at the Ortigia Academy of Magic, aspires to become a powerful sorcerer. But he is unable to become one as, despite his excellent grades and strong commitment to his studies, he fails his summoning class. With the threat of repeating a year hanging over his head, Alto tries following an old, worn-out grimoire in a desperate attempt to resolve his situation. To his surprise, he succeeds and summons a powerful demon named Vermeil. As a sign of gratitude for releasing her, Vermeil agrees to become Alto's familiar, sealing their relationship with a deep kiss. Little does Alto know what else he is capable of and what Vermeil's past hides.

After finishing their "debut," Kate, Emilico and three other pairs who started with them begin a new life as adults.

Listless geek Mizuto Irido and introverted nerd Yume Ayai seemed like a match made in heaven, connected by their mutual love for literature. Unfortunately, their differences gradually grew, and they separated just after their middle school graduation. But, as if by divine comedy, the two find themselves reunited as step-siblings. A rivalry begins to brew between the former couple, both unwilling to acknowledge the other as the older sibling. In an attempt to "solve" this issue, Mizuto and Yume agree upon a rule: whoever crosses the boundaries of siblinghood norms loses, and the winner will not only be called the older sibling, but also get to make a request. However, now that they live under the same roof, the lingering memories they share start to influence their actions—possibly rekindling the feelings that may not have been fully extinguished in the first place.

At the beginning of chaos, the world was divided into three realms: the realm of deities, the realm of men, and the realm of demons. The realm of deities sent a spirit seed down into the world to help the common people. But the spirit seed continuously absorbed the evil of the world and cruelly harmed living things. In the end, Sen Luo, the king of the deities, sacrificed himself and sealed it. However, because of it, the Shangqing Xianmen, where the realm of deities is located, gradually waned and was lost in history. A thousand years later, the ruins of Shangqing Xianmen started to appear in succession. All major sects fought their hardest for possession of the treasures in the ruins.