Haruka Mizuhara serves as a stepmother figure, driven by her deep desire to be accepted as a true parent by her stepchildren. She possesses long, wavy violet hair, often styled in a braid or parted to the side, and green eyes, complementing her slim, pale build. Her attire frequently blends domestic elements like aprons with miniskirts or shirts, reflecting her housewife role.

Her background centers on persistent efforts to forge a maternal bond with her stepdaughter, Chisa, who consistently rejects these attempts. This rejection fuels Haruka's primary motivation: achieving recognition and emotional connection as a mother despite lacking biological ties. A pivotal incident occurs when another stepchild, Takumi, sexually assaults her. This trauma triggers a significant psychological shift, resulting in a disoriented mental state dominated by an obsessive focus on sexual activity.

Following the assault, her behavior undergoes a drastic transformation. She becomes fixated on using sexual intimacy as a misguided method to demonstrate maternal devotion to Chisa, believing this approach will finally earn her stepdaughter's acceptance. This altered state defines her subsequent interactions and development, marking a profound departure from her initial efforts to build familial harmony through conventional caregiving.