Saizou is a 14-year-old girl who presents herself as male, a disguise rooted in her background within Japanese theater traditions that forbade female performers. This presentation was enforced by her homosexual father, who raised her with masculine behaviors and attire. Her father perished in a theater fire on her 13th birthday, an event she witnessed after accidentally encountering him with his lover, causing her profound trauma. She interprets her name, Saizō—associated with the Japanese word for "sin" (罪, tsumi)—as evidence of inherent sinfulness, resulting in deep-seated guilt and self-loathing. The fire occurred one year prior to the story's beginning.

In combat, Saizou wields a specialized paper fan that unfolds into an elongated paper rope, capable of temporarily restraining supernatural entities called Yōi. She also inherited a ritual dance from her father, historically linked to the myth of luring the goddess Amaterasu from her cave. This dance actively attracts Yōi. Her character arc centers on reconciling her perceived sinfulness with her identity.