The story begins with the protagonist, a hero summoned to the world of Nextmarch, finally defeating the Demon Lord after two years of arduous training and constant battles. Exhausted and depleted of all magic, he collapses, only to be greeted by the voice of Princess Fols A. Prill, the one who summoned him. Fols, a key figure in his summoning and a powerful individual, expresses her gratitude, but before she can heal him, a magic circle appears beneath the hero, signaling his return to his original world. Despite Fols' desperate pleas, he is whisked away.
He awakens to find himself back in Japan, but it's not the Japan he remembers. The sky is an unnatural red, buildings are in disrepair, and monstrous, one-eyed giants roam the streets. Before he can process this disturbing reality, he is attacked and sent flying by a giant. Realizing he has lost his heroic powers and the magic of this new world is absent, he despairs. However, a sudden mental prompt activates a "Status Effect," revealing a game-like interface with his stats and skills. Among his unique skills, he discovers "Ice God Awakening." Recalling Fols' words about him possessing two opposing powers, he realizes this is the dormant ice power he never chose. With newfound resolve, he unleashes "Ice God Awakening" and a powerful ice spear, defeating the giant.
Confused by this altered Japan, where monsters and status effects are real, he finds a young woman in fantasy attire, also seemingly out of place. He is then rescued by a group who identify themselves as the Shinjuku Dungeon Exploration Team. He learns from their leader, Jurai, that this world was transformed ten years prior by a "Dungeon Impact," where dungeons appeared and humans gained "Status Effects" to fight monsters. Those caught in the initial dungeon appearances are called "Lost Children." Jurai explains that the protagonist, a "Lost Child," is likely the sole possessor of the "Braver" class, a unique and powerful designation. He also discovers he has inadvertently defeated an area boss, a feat unheard of for a Level 1 individual.
Jurai becomes his guardian, and the protagonist, now identified as a "Lost Child," is granted adventurer status. He learns that his family died in an accident before his summoning, but he holds onto the hope of finding a way back to his original world. He decides to become an adventurer, believing it's the best way to utilize his newfound powers and potentially find clues to return home. Two weeks later, he embarks on his first official dungeon quest, a beginner-level dungeon. He is surprised to learn that a senior adventurer is assigned as an observer for his first mission, and it turns out to be a grumpy young girl.
