Yaku displays distinctive green hair cut to shoulder length and red eyes, appearing as a teenager. Her figure includes notably large breasts, a trait that becomes a recurring point of envy for Miko. Her overall demeanor projects a mature air, contrasting with others.

A defining trait is her curse: during full moon nights, she undergoes involuntary transformation into a werewolf unless she achieves orgasm beforehand. This shapeshifting introduces significant narrative tension and personal vulnerability. Her sexuality is highly active, with a noted preference for relationships with "yankee"-style delinquent young men. Reports suggest these partners often struggle to match her intense carnal urges.

Her combat abilities as a ninja are acknowledged as powerful, though specifics about techniques are not detailed beyond the inherent threat of her werewolf state. Her narrative role centers on her alliance with Miko following the clan's destruction and interactions driven by her condition and personality.