The story begins with Kondo Shun, a somewhat introverted high school student, noticing a strange light emanating from the classroom floor. Before he can react further, the light intensifies, engulfing the entire classroom in a blinding flash. The sudden event causes panic and confusion among his classmates, who are unable to see or escape. The light then spills out of the classroom, and silence falls.
Shun wakes up in an unfamiliar, grand hall, realizing he is no longer in his classroom. The hall is vast, with ornate murals and a large chandelier, reminiscent of a European museum or church. He finds his classmates scattered and unconscious around him. His close friend, Asano Yuma, wakes up beside him, and together they begin to rouse the others. They speculate about being kidnapped, but the absence of any captors is puzzling.
As they wake everyone, Shun encounters Minezaki Karin, the school's most popular and beautiful student, who has always shown him kindness despite his ostracized status due to bullying. He harbors a secret crush on her. He also notices that many of his classmates, while not actively participating in his bullying, largely ignore his plight, except for Yuma and Karin.
Their confusion is interrupted by a commanding voice. A regal-looking old man, who appears to be a king, addresses them as "saviors." He apologizes for the abrupt "kidnapping," explaining that they were summoned to find seven legendary swords, each possessing immense power, which the "Demon Lord's Army" is also seeking. To prove his point, the king shows them a horrifying vision of a bull-man brutally killing a knight, convincing them of the grim reality of their new world.
The students are initially skeptical and angry, but the king explains that the "Demon Lord's Army" is a unified force of monsters and demons that has been indiscriminately attacking and demanding submission from neighboring countries. He reveals that their world is at war and that the seven swords are crucial to preventing the human race's extinction.
Yuma, inspired by the prospect of adventure and a life with purpose, rallies the students to stay and fight. Most of the class, including Karin, agrees. Shun, initially hesitant, is also persuaded. They are then tasked with determining their classes and abilities using a crystal. Shun discovers his stats are perfectly balanced but his unique skill, "Status Ailment Doubling (Lower)," is a double-edged sword, potentially amplifying negative effects. Yuma, on the other hand, receives the "Swordsman's Memory" skill, indicating a warrior path. Karin's unique skill is "Goddess's Healing (Lower)."
The king then assigns them mentors: veteran knights, mages, adventurers, priests, and assassins. Shun is surprised to be assigned to Alicia Reis, a skilled magic swordsman, as his mentor, despite his "Dark Knight" class, which is typically associated with demons. The king explains that Shun's class is likely a result of his transfer from a peaceful world where demons are considered myths.
The next day, Shun begins his training with Alicia in the mountains. Their first session involves a mock battle where Shun is quickly defeated, highlighting his lack of combat experience. Despite his initial struggles and the pain of training, Shun is determined to improve.
Meanwhile, Karin, who has developed feelings for Shun, is encouraged by her friend Yuuna to pursue him. During a welcome banquet for the transferred students, Shun is drawn to a beautiful, hidden lake by a mysterious singing voice. He encounters a girl who disappears, leaving him with the impression that the lake is connected to her. He shares this discovery with Karin, and they promise to return.
The story also introduces Prince Seel, who views the transferred students with disdain and intends to crush them. The "Demon Lord's Army" is also actively seeking one of the legendary swords, indicating escalating conflict.
The narrative follows Shun's journey as he adapts to this new world, grappling with his unusual abilities, forming bonds with his classmates, and facing the looming threat of the Demon Lord's Army. His relationships with Karin and Yuma begin to deepen, while the mystery of his own powers and the true nature of this world unfolds.
