Yu arrives at a mansion as an orphan, burdened by complete amnesia regarding her past and dependent on Master Renji for shelter. Within the mansion, she exists under Renji's control, subjected to sexual exploitation alongside other women. She complies with his demands to maintain his favor, though she occasionally questions his treatment of the others despite her general obedience and efforts to appease him.

Her existence involves enduring extreme physical and psychological abuse, including systematic rape, torture, dismemberment, and forced participation in acts involving bodily waste, all within a context of severe power imbalance and institutionalized cruelty.

Yu has a younger sister who also suffers within the mansion, particularly when events deviate from Renji's expectations; the sister's fate remains tightly bound to Yu's compliance and the master's arbitrary punishments.

Available media documents no significant character development or redemption for Yu. Her narrative primarily illustrates victimization within a framework of non-consensual BDSM and extreme fetishism, concluding without resolution for her memory loss or liberation from the oppressive system.