After the death of his grandfather, 19-year-old Kazuya Souma—an aspiring civil servant—is left all alone with no one to call family. Out of the blue, he is transported to the Elfrieden Kingdom, a small ailing country in another world, to be a hero. An ongoing war with the demon army has put the entire world in peril, and Kazuya was summoned to aid in the conflict as an offering from Elfrieden to its allies. Dissatisfied with being used as tribute, Kazuya decides to help the kingdom revamp its declining economy—not by way of adventuring or war, but through administrative reform. Abruptly declared the King of Elfrieden and betrothed to the princess, the Realist Hero Kazuya sets out to assemble a group of talented citizens who will assist him in his bureaucratic battles to get the kingdom back on its feet.

All his life, Yuuya Tenjou has been the subject of resentment and contempt from everyone around him, even from his parents. To make matters worse, his grandfather—the only person who ever showed him affection—suddenly dies, leaving Yuuya truly alone. Despite facing many adversities, Yuuya does what he can to offer kindness to those who need it—but even the most good-natured people can only tolerate so much abuse. Just when he reaches his breaking point, a flicker of hope appears in the form of a hidden door in his bathroom. This door provides two-way access to an abandoned house in another world, where he instantly gains game-like stats and skills. Moreover, the house once belonged to a sage, which gives Yuuya access to remarkable weapons, equipment, and crops with extraordinary effects. With these newfound blessings, the once-undesirable Yuuya may just reach his true potential and become unstoppable.

On her way to school one day, Suzume Iwato stumbles upon Souta Munakata, a young man searching for abandoned areas. The high school girl directs Souta to a nearby ruin, but out of pure curiosity, she herself decides to head to the same destination. Once there, Suzume discovers an isolated door with a dreamlike universe lying beyond it—a place that she can see and feel, but not enter. A strange stone rests on the ground nearby, but it turns into a cat-like creature and scurries away when Suzume lifts it. Suddenly afraid, she heads back toward her school, not realizing that her act of leaving the door open will have consequences. With the keystone released, the evil within the other universe can now freely escape and wreak havoc throughout Japan. Intending to correct her dangerous mistake, Suzume joins Souta—whose true goal is to prevent evil from festering—in finding and locking all open doors before the country is destroyed.

Despite his noble title, Noir Stalgia is at the bottom of the social hierarchy. Because of this, his fellow nobles oppress him and treat him like garbage. However, he possesses a rare yet powerful ability to communicate with the Great Sage, an oracle who grants Noir the answer to absolutely anything. After failing to secure a job as a librarian, Noir decides to join the Hero Academy. He knows he must become stronger to enter the institution. The Great Sage advises him to explore a hidden dungeon deep within the mountains. There, Noir meets Olivia Servant, a beautiful yet enchained maiden trapped within the labyrinth. Olivia bestows upon Noir a set of ridiculously powerful skills that grants him virtually total control over reality. Naturally, there is a catch—every time Noir attempts to use his powers, his life points decrease, putting his life at risk. To replenish his energy, he must give in to worldly pleasures such as kissing his childhood friend! With his newfound powers, Noir begins his journey as a student in the Hero Academy, meeting new acquaintances and helping them through the dire situations ahead.