In the modern world, a colossal tower known as “Tengoku” (Heaven’s Prison)—a dungeon that pierces far beyond the Kármán line—looms over Japan. In this era, people can make a living through brute strength by wielding “Demon Swords”, blades imbued with the power of devils. As many young people dream of becoming “Demon Swordsmen”, Jinya Kochō shows little interest. Instead, he spends his days doing part-time jobs for a shady employer. One day, Jinya accidentally comes into possession of a demon sword and finds himself thrust into the world of demon swordsmen. As he slays the monsters of Tengoku, stealing their power and sharpening both his sword and himself, he begins to uncover unsettling truths— The strangeness of his own demon sword, and the reason why these monsters bear the names of angels…