"Change 123" is a manga series that blends action, comedy, and psychological drama, centered around the life of Motoko Gettou, a high school girl with a unique condition. Motoko suffers from dissociative identity disorder, resulting in three distinct personalities that emerge under specific triggers. Each personality possesses its own set of skills and traits: Hibiki, a calm and analytical martial artist; Mikiri, a cheerful and flirtatious girl with a knack for acrobatics; and Fujiko, a cold and ruthless fighter with a penchant for violence. These personalities were artificially created through a secret government project known as "Change 123," which aimed to develop superhuman soldiers.

The story begins when Motoko meets Hiromi Kosaka, a martial arts enthusiast who becomes entangled in her chaotic life. Hiromi discovers Motoko's condition after witnessing her personalities switch during a confrontation. As their relationship develops, Hiromi becomes a stabilizing force for Motoko, helping her navigate the challenges posed by her condition. However, their lives are further complicated by the reappearance of Motoko's estranged father, Kenzo Gettou, who is revealed to be the mastermind behind the "Change 123" project. Kenzo seeks to reclaim Motoko as his ultimate weapon, leading to a series of intense confrontations.

Throughout the series, Motoko and her personalities must confront their shared past and the trauma that shaped them. The narrative explores themes of identity, family, and the consequences of human experimentation. Supporting characters, such as Hiromi's childhood friend Sayaka and various adversaries tied to the "Change 123" project, add depth to the story, creating a dynamic interplay of alliances and rivalries. The manga balances its darker themes with comedic moments, often stemming from the contrast between Motoko's personalities and their interactions with Hiromi.

The action sequences are a key element of the series, showcasing the unique fighting styles of each personality. Hibiki's precision, Mikiri's agility, and Fujiko's brutality are frequently highlighted in battles against opponents ranging from street thugs to highly trained operatives. These confrontations drive the plot forward while also serving as a means to explore the psychological and emotional struggles of the characters.

As the story progresses, Motoko and Hiromi work together to dismantle the remnants of the "Change 123" project and confront Kenzo's machinations. The series concludes with a resolution that ties together the personal growth of the characters and the overarching conflict, offering a satisfying conclusion to the narrative. "Change 123" stands out for its unique premise, blending action-packed sequences with a heartfelt exploration of identity and relationships.