"La Blue Girl" is a manga series that blends elements of supernatural horror, eroticism, and action. The narrative centers on Miko Mido, a young kunoichi (female ninja) from the Mido Clan, a lineage tasked with protecting the human world from demonic forces. Miko inherits the role of the clan's leader after her father's death, despite her initial reluctance and lack of confidence. Her journey involves mastering her clan's ancient techniques, which include the use of sexual energy to combat and subdue demons.

The story unfolds as Miko faces the resurgence of the Demon Realm, a parallel dimension inhabited by malevolent entities seeking to invade the human world. The demons, led by the powerful and sadistic Lord Kuromatsu, aim to harness Miko's unique abilities to open a portal between the two realms. Miko's struggles are further complicated by her encounters with various demons, some of whom seek to corrupt or exploit her, while others form uneasy alliances with her.

Miko's training and battles are intertwined with her personal growth, as she learns to embrace her role and the responsibilities it entails. Her relationships with other characters, including her mentor, Jaku, and her rival, Ran, add depth to her character and the narrative. The series explores themes of power, sexuality, and the duality of human and demonic nature, often through intense and graphic confrontations.

The plot is driven by a series of escalating conflicts, culminating in a climactic battle between Miko and the forces of the Demon Realm. Throughout the series, Miko's resilience and determination are tested as she navigates the treacherous landscape of her dual existence as both a protector of humanity and a target for demonic forces. The manga balances its darker, more explicit elements with moments of character development and world-building, creating a narrative that is both provocative and engaging.