Spellblades are a dangerous and irreversible technique in the world of magic, their secrets shrouded in mystery with only their deadly power known to the public. Each year, the prestigious magic school Kimberly welcomes new students with a grand parade featuring magical beasts. Among the newcomers is Oliver Horn, who becomes intrigued by a girl wielding a Japanese sword and dressed in unique attire. However, he soon discovers that the academy is far from ordinary as labyrinths, monsters, and other dangerous entities begin to threaten the student body. Nanatsu no Maken ga Shihai suru follows the intertwined fates of two warriors as they uncover the dark truths hidden within Kimberly's walls.