Fubuki Kai is a blonde-haired, blue-eyed young woman who first appears as a transfer student at Miko Mido's junior college. At sixteen years old, she balances her life as a high school student with her chosen path as a ninja warrior. Unlike Miko, who was born into the hereditary Miroku ninja clan, Fubuki is a self-made ninja who trained herself in various forms of ninjutsu. Her background is marked by personal hardship, as she came from a broken family and immersed herself in stories of ninjas and feudal Japan to escape the difficulties of her everyday life.

Fubuki′s primary motivation is her intense drive to prove herself as the greatest ninja in the world. She becomes deeply resentful of Miko Mido, perceiving her as someone who had everything handed to her by birthright and who was placed on a pedestal by others. This resentment fuels her initial role in the story as a determined rival who sets out to destroy Miko′s reputation and surpass her in every way. Fubuki′s actions demonstrate both cunning and recklessness; she hypnotizes a teacher into stealing Miko′s ninja scrolls to gain access to the Shikima realm, a parallel dimension of demons. Once there, she defeats the Shikima King′s minions and attempts to persuade the King to make her the new queen of the realm.

Her rivalry culminates in a final battle against Miko in front of the Shikima King, during which Fubuki is defeated in a sexual duel. This defeat marks a significant turning point in her character development. Rather than maintaining her hostile stance, she shows respect for Miko as the true master of ninjutsu, and the two become friends almost immediately afterward. Following her defeat, Fubuki is adopted by the Shikima and undergoes a transformation that makes her a half-Shikima, half-human hybrid, similar to Miko. This transformation grants her additional power, including the ability to transform into a beast known as Shikima Mode, and she expresses fondness for her new demonic form.

Even after becoming an ally, Fubuki maintains a competitive dynamic with Miko and occasionally irritates her by demonstrating superior proficiency in certain situations. Their friendship proves genuine, as Fubuki remains loyal and never leaves Miko′s side in times of need. Fubuki′s role expands beyond the original series into sequels such as La Blue Girl Returns and Lady Blue, where she continues to fight alongside Miko against threats such as the Mahoroba butterfly demons and cursed flutes that endanger both the human world and the Shikima realm.

Regarding her abilities, Fubuki is a highly skilled ninja whose self-taught training allowed her to surpass many established schools of combat. She possesses powerful hypnotic abilities, capable of making people believe almost anything or become aroused simply through her gaze. Her mastery of sexcraft ninjutsu, a form of erotic combat common to the Miroku tradition, allows her to use sexual techniques as weapons against opponents, though this carries the risk of losing oneself to pleasure during battle. After her transformation into a half-Shikima, her physical capabilities are enhanced even further, granting her demonic strength and the aforementioned beast transformation. Despite her formidable powers, her defining character trait remains the fierce, uncontrollable spirit that drove her from a difficult childhood to challenge and ultimately stand beside one of the most powerful warriors in her world.