The beginning of Light Magic and the Hero, an otome RPG, unfolds fairly normally: the heroine, Alicia Ehnleit, meets her three love interests one after another and then inevitably comes face-to-face with the villainess. Yumiella Dolkness may be of noble descent, but her dark hair and rare dark-type magic—both associated with the Demon Lord—spark fear in anyone who sees her. When she is five years old, Yumiella regains memories of her previous life in modern Japan, also realizing that her fate is to become the hidden boss that appears after Alicia and her suitors defeat the Demon Lord. Yumiella refuses to live as the game dictates and, as she prefers the game's fantasy elements over its romance, she decides to cultivate her magical skills and level up in secret. However, everything falls apart on the day of the Royal Academy's entrance ceremony. Yumiella's powers are measured at level 99—something thought impossible even for the royal knights, let alone a 15-year-old girl. With the royal family requesting her help, and everyone else insisting that she prove her strength, Yumiella realizes that her dream of a quiet life is no longer an option.

Sasaki, a 39-year-old corporate employee, has resigned himself to live a modest life without dreams and dangers. To his great surprise, his fate takes a brutal turn after he decides to adopt a Java sparrow that he names Pii-chan. The talking bird not only happens to be a reincarnation of a famous magician from another world, but it decides to grant some of its powers to Sasaki—along with the ability to traverse between worlds. Sasaki begins a lucrative business of selling technological items from his world to the less advanced civilization of the other. However, Sasaki's life becomes more chaotic when he stops an attempt on a woman's life with his new powers. Unfortunately, the woman Sasaki saved also happens to be a government agent named Hoshizaki, who is tasked with tracking down gifted individuals like him. Forced to join Hoshizaki's secret agency, Sasaki partakes in dangerous missions to find other gifted criminals. He does not even have the luxury of hiding in the other world, where a war is about to break out. If he wants to protect peace in both worlds, Sasaki will have to become the hero that no one expects him to be.

A decade ago, princess Krystal Novaty “Hime” Nokanatika traveled from another world to escape assassination attempts by an evil force. When she arrives in modern-day Japan, she encounters Haruto Satou. With him she shares a promise: he must forget what he has just witnessed, and the two will become friends. Now heading back to the Nokanatika Kingdom to fulfill her royal duties, Hime bids farewell to Haruto. However, when the young man suddenly remembers his first meeting with Hime, he rushes to the location where she first appeared and crosses the dimensional portal to be reunited with her. His arrival disrupts the marriage ceremony between Krystal and prince Marmarugias Gisaras. The wedding is brutally interrupted by the attack of an abyss monster who threatens the princess' life. Acting impulsively, Hime decides to exchange rings with Haruto, which grants her new husband light powers that permit him to slay the monster. Now dubbed as the Ring King, Haruto must marry four other princesses to acquire new magical powers and have a chance to prevail in his fight against the enemy of the world: the Abyss King.

After the climactic battle to decide the fate of humanity, the hero Max, alongside his party, emerges victorious against the formidable Demon Lord. As he draws his last breath, the defeated Maou vows to return more powerful than ever to take his revenge. Ten years later, although Maou has resurrected, the process is incomplete, resulting in him taking on the form of a child. Nevertheless, not wanting to waste another second, Maou pays his nemesis a visit—but the hero who once gallantly protected humankind from the demon's clutches is now a pitiful slob bearing no resemblance to a man of his former caliber. Despite his disappointment, Maou moves in with Max in hope of building him back up into a worthy adversary. But as the demon learns more about the events that transpired in the decade of his absence, he realizes that there is a story behind Max's downfall that he knows nothing of.