Change 123 is a manga about a high school girl named Hibiki who has three distinct personalities, each with different combat skills and memories. When her classmate, Takamichi, discovers her secret, he becomes drawn into her life and tries to help her uncover the mystery behind her condition. Readers enjoy the series for its blend of action, comedy, and harem elements, as well as the unique premise of fighting personalities that must coexist and protect one another.