Hiroki Yamada, a 15-year-old freshman step into Sakuragawa High School with a burning passion for music, fueled by memories of his late older brother, Kaito Yamada, who taught him guitar and singing. Inspired by bands like Muse, Deftones, Radiohead, and so on.

On his first day of entrance, a peculiar girl with a black surgical eyepatch named Aoi Mizuno "The Priestess" confronts him, declared him as the "Dark Lord of Tartarus" from their middle school roleplaying days. This encounter drags Hiroki’s cringeworthy chuunibyou past into the present, setting the stage for a heartfelt and comedic music-driven journey.

Joining the Light Music Club of Sakuragawa, Hiroki navigates friendships, lingering grief, and his reawakened chuunibyou tendencies, culminating in a transformative performance where he channels his inner "Dark Lord" on stage.