Nanaka Koyo is a third-year middle school student living in the modern Reiwa era. She wanders into an unfamiliar world through the gates of the Gogyo Shopping Street and meets a young man named Mao. After defeating a demon that attacked Nanaka, Mao tells her, "You're a demon, aren't you..."

Nanaka, who doesn't die even when she touches Mao's "Sword of the Destroyer Star," may have been cursed after being exposed to the blood of a cat demon when she was a child. Nanaka returns to the modern Reiwa era and begins investigating the accident that happened to her eight years ago.