The story begins with a secret ritual in a hidden chamber beneath a cathedral. Four young women in thin white robes, one with light blue hair who appears to be the leader, perform a summoning ceremony. They chant prayers to the Holy Goddess Sophia, seeking her aid in their time of crisis. The narrative explains that "Hero Summoning" is a secret art to call powerful individuals from other worlds, who are then bestowed the title of "Hero" by the world's system. While this world also has its own Heroes, those summoned from other worlds are significantly stronger due to a power imbalance between worlds. This world was constructed based on creations from the summoned Heroes' home worlds, making it a "lower world" compared to theirs. When individuals cross world boundaries, they receive power-ups and skills to maintain the conceptual hierarchy.
The summoned individual is Shido Reiji, an eighteen-year-old high school student who finds himself in a dark void. A disembodied voice informs him he has been chosen for an inter-world summoning and offers to grant him powers. Reiji, overwhelmed and confused, tries to protest, but the voice proceeds to grant him powers, including enhanced physical abilities, before sending him away. The voice reveals that Reiji is being sent to a "lower world" based on human creations and expresses anticipation for what he will "mess up."
Reiji awakens in a grand hall, finding himself before the four summoning maidens and a group of robed figures, including an elderly man identified as Pope Altorius IV of the Holy Light Church. He is bewildered by their attire and the situation, especially when the blue-haired maiden, who is revealed to be a summoner, approaches him. Her revealing ceremonial attire, designed to impress summoned Heroes, causes Reiji to blush. The Pope explains that they summoned him, a Hero from another world, to save them from a dire situation. Two years prior, an evil god revived, empowering demons and causing unrest. The Holy Light Church intends to lead the world and defeat the evil god and the Demon Lord.
When Reiji protests that he lacks such power, he instinctively raises his hands, and a burst of flame erupts, scorching the Pope's throne and hair. The Pope, enraged, declares Reiji an impostor and a servant of the evil god. Reiji, shocked by his own uncontrolled power and the accusation, flees, discovering his enhanced physical abilities allow him to escape the guards. He bursts out of the cathedral and into the bustling city of Luxiria, the capital of the Holy Light Church.
While fleeing through the city, Reiji is pursued by guards. He manages to evade them by leaping over gates and using a horse-drawn carriage to escape the city. He finds himself in a forest, where he is attacked by a pack of Forest Wolves. Just as he is about to be overwhelmed, he is inexplicably transported to a vast grassland. There, he encounters a giant boar-like monster, a Giant Hornboar, which he also narrowly escapes thanks to an unexpected electrical discharge from his hands.
He then meets a young blonde girl named Tena, who uses dark magic to defeat the monster. Reiji, still confused about his powers and his situation, learns from Tena that he is in a different world and that she serves a mysterious woman named Anri. Tena invites Reiji to Anri's mansion, the Black Rose Mansion, for safety.
At the mansion, Reiji meets Anri, a masked woman with immense power. He explains his predicament, and Anri reveals her own extraordinary past: she was a human sent to this world by an evil god, who subsequently became a literal evil god herself. Anri explains that returning to Reiji's world is only possible by completing trials set by three world administrators, the first being to gain the recognition of the Demon Lord. Anri also reveals that Reiji's powers, including the uncontrolled magic and teleportation, are likely due to the evil god's influence.
Anri grants Reiji a "Status" window, revealing his skills: "Auto Magic," "Random Summoning Possession," "Swordsmanship," "Light Magic," and "Item Box." The "Auto Magic" skill explains his uncontrolled magical outbursts. Anri also reveals that Reiji's "Item Box" contains a "Sword of Chance," "Leather Armor," and a "Letter from the Evil God." The letter details the trials and hints at the evil god's manipulation.
Anri, Tena, and Reiji prepare for his journey. Anri imposes a peculiar condition for Tena's accompaniment: Reiji must wear a ridiculous outfit and hold Tena's robe to prevent him from being separated by accidental teleportation. They also learn that Anri is the revered figure of the "Holy Anri Kingdom," and her statue is a prominent landmark. Tena is given a magical crow as a watchdog to monitor Reiji. They head towards the city of Anria, where the dungeon is located, to begin Reiji's quest.
