When a second moon mysteriously appears in the sky, strange creatures known as Vivids appeared all over the world. In order to fight and survive the Vivid’s destructive tendencies, humans developed super powered weapons, and thus, the legendary heroes they called Wielders were born!

Devastated over her mother’s death, Sora Bellarose sets out to find the Vivid responsible. When she meets Damian Delfuego, she finds that he too is looking for the same monster, but to avenge his late mentor. With the same goal in mind, she joins him at a Wielder Detective Agency. There she meets the powerful but also distrusting members of Weapon City, so to prove herself to them, she aids the squad in their current mission, to solve the case behind the mysterious monster troubling the city of Alto Reo — The Billion Beast!