Lady Iku is the concubine of Kogan Iwamoto, the master of the Kogan school of swordsmanship. She is introduced as a long-suffering woman who initially appears resigned to life under his control. Her background is marked by persistent social stigma; from a young age she was the subject of a derisory children's song, and the local populace would flee at her approach. This ostracism stemmed from a belief that coming into close proximity to her would result in a cursed and painful death, a superstition reinforced by past incidents in which men mysteriously died while in her company. The public scorn and isolation she endured only increased her dependence on her husband.

Iku's personality is shaped by this history of rejection and subjugation. She is portrayed as a victim of her circumstances and a reflection of the brutal social realities of the period. Her motivations are largely tied to survival and navigating the dangerous environment created by Kogan's possessive and violent nature. Any man who even looked at her could expect terrible retribution from Kogan, which further deepened her isolation and rendered her a figure of fear and pity.

Her role in the story is that of a supporting character whose presence underscores the cruelty and moral decay within the Kogan clan. Key relationships include her complex and abusive bond with Kogan, through whom she has also likely lost multiple fiancés, adding a layer of personal tragedy to her situation. This deception and loss provide her with a strong justification for revenge within the narrative, aligning her with other characters who have been grievously wronged. Her development, while limited, illustrates the oppressive forces that shape her actions and reinforce her status as a tragic figure caught in the violent power struggles of the samurai world. She does not possess combat abilities but exerts influence through her position as Kogan's concubine, however constrained that role may be.