Yaya is a shy, quiet teen with a passion for singing, Japanese rock music, Gothic Lolita, cosplay and music in general. But she has a secret: When she looks in a mirror or hits her head, Yaya's second personality, aptly named Nana, takes over her body and puts the wrong-doers in their places, shouting her catchphrase "Heavenly Punishment!" and once the damage is dealt, "Justice is done!"

The series chronicles Yaya and Nana's somewhat episodic adventures against bullies, perverts, and generally mean people. The manga also has a lot to do with music, as several of the characters have connections to the music industry or play in a band.