Sachiko Tanaka attends Goryoukan Academy as a reserved student marked by quiet demeanor and introspective tendencies. Her full name, 田中幸子, merges the common surname Tanaka ("dweller in the rice fields") with the given name Sachiko ("child of happiness" or "child of good fortune"), subtly mirroring her solitary nature and quiet perseverance. She possesses a slender frame (165.3 cm tall, 85/59/81 cm measurements) with sleek grey hair styled in a ponytail accented by ribbons, complemented by pale grey eyes.

Operating covertly as the Black Swan Knight, she serves as a Striker tasked with neutralizing interdimensional entities known as Oburi. Preferring solo missions, her combat methodology reflects a deliberate emotional detachment, avoiding alliances to shield herself from vulnerability. Official profiles note heightened sensory perception and physical endurance, offset by modest social skills and academic performance.

Though habitually isolated, she intervenes in critical battles—such as aiding the Altair Torte unit—with swift precision, demonstrating tactical acumen and martial prowess. Her fleeting collaborations underscore a willingness to support allies during existential threats while preserving personal boundaries.

Existing records omit specifics about her family history, life prior to the academy, or evolution across storylines. Documented appearances remain confined to her niche within the Fifth Force structure as a solitary combat specialist, with no expanded media exploring her role beyond these engagements.