In the Dark Century, humanity suffers under the tyrannical rule of the devil Vandel, who can command monsters. The Vandel Busters, a group of heroes who hunt these devils, consider the Zenon Squad the continent’s most formidable team. Young Beet, an aspiring Vandel Buster, dreams of joining the Zenon Squad. A mistake on his part leads to the squad’s defeat at the hands of the devil Beltose. As the five dying Busters expend their remaining life force into their unique weapons, the Saiga, they entrust these weapons to Beet before succumbing. Years later, Beet embarks on a quest to honor the Zenon Squad’s legacy and bring an end to the Dark Century.