The story follows the hero known as the Sage, Seed, who sacrificed his life to save the world after a final deadly battle with the Demon King. While in the space between the living and the dead, the outer god Afeldoose informs him that the Demon King is going to revive. To face this threat once more, Seed is reincarnated back into his original world as a student at the Eldion Royal Magic Knight Academy.

The central conflict arises from the impending return of the Demon King, forcing Seed to navigate a second life while secretly possessing the wisdom and power of his previous existence. The setting is a high fantasy world with a formal academy designed to train elite magic knights, where students are segregated by social status, with nobles placed in the A class and commoners in the F class.

Seed is a former villager without a surname who was one of the legendary Five Heroes that defeated the Demon King 15 years ago. Afeldoose is a long-haired female deity who uses a masculine first-person pronoun and is responsible for reincarnating Seed using a different body. The other members of the Five Heroes include Iris Sereno, a quiet female swordsman and the group's leader who has been missing for over a decade; Veronica Redbelt, a red-haired elf sword saint with immense strength who now works as an educator; Fikes Maletra, a paladin who served as the party's vanguard and now leads the Holy Knight Order; and Cattleya Wizlaril, a saint who specialized in recovery magic. Sirius Nordens, a commoner himself, serves as the teacher for the A class at the academy and holds a grudge against the reincarnated Seed.

The narrative follows Seed as he begins his second round of adventures, reuniting with his former comrades and meeting new classmates at the magic knight academy, all while preparing in secret for the prophesied return of the Demon King.