Ushio Aotsuki (voiced by Yuu Hatakenaka) is an ordinary middle school student with a frail body. By chance, Ushio met a monster that had been sealed for 500 years in the basement, and accidentally pulled out the "beast grass" that sealed it, allowing the monster to return to the world. The amazing power that burst out from Ushio shocked the monster, and it immediately expressed its submission to Ushio, so Ushio named the monster "Tiger" (voiced by Rikiya Koyama). As the heir of the beast grass, Ushio shouldered the mission of slaying demons and maintaining peace, and various monsters followed and challenged him. In the constant cooperation and fighting, Ushio and Tiger formed a deep friendship, and the two were also involved in a conspiracy that affected the whole world, and the various people hiding behind the beast grass also appeared one by one beside Ushio.