Takashi Suzuki, a 42-year-old former hitman and mercenary, has lost his long battle with cancer. However, death is not the end for a killer of his caliber. A mysterious goddess intervenes, offering him reincarnation in a fantasy world not for salvation, but for a contract: eliminate thirty-two individuals designated as heroes. These are not noble champions but Japanese high schoolers summoned en masse and granted excessive cheat-like powers, whose unchecked rampage is plunging this new world into chaos.

Reborn as Rei in a younger, magically-attuned body, he is partnered with Lydina, a beautiful and deadly elf warrior. To complete his divine kill order, Rei must rely on a hybrid combat style, blending modern tactics from his previous life, the classical martial art Shingu-ryu, and newly awakened magic. His targets include a Sword Saint, an Arch Sage, and a Necromancer, each a catastrophic threat in their own right.

After proving his capabilities in the Republic of Zirtlo, Rei and Lydina receive an S Certification from the Adventurers Guild. This achievement, however, brings unwanted scrutiny in the form of an official appraiser named Eve, a blue-haired woman with an eyepatch. Recognizing Rei as an apostle of the goddess, Eve becomes a devoted follower and joins the party. The trio then travels to the dwarven kingdom of Mergid to prepare their equipment, only to find a new group of explorer-class heroes already there. What begins as a targeted elimination escalates into a massive defensive battle for the entire kingdom, forcing Rei to coordinate with powerful dwarf-operated magic cannons and golem squads to protect Mergid from the summoned interlopers. As Rei systematically works through his list, the goddess's true motives remain shrouded, and a larger conspiracy behind the summonings themselves begins to surface.