Dame Iku is introduced as the long-suffering concubine of Kogan Iwamoto, the grandmaster of the Kogan-ryuu sword fighting school. Her role within the household is one of considerable hardship, as she is treated with little value by Kogan, who sees her primarily as a possession. This dehumanizing existence is compounded by a cruel rumor that has left her isolated from the community; she is believed to be cursed, and people flee from her presence in public, such as when she visits a bathhouse.

Iku's personality is shaped by the profound loneliness and resignation that result from this treatment. She has come to believe that her very nature is a curse, as two men she was previously engaged to died under mysterious circumstances. This deep-seated insecurity and self-doubt define her demeanor, making her appear fragile and burdened by guilt. Despite her oppression, she possesses a quiet inner strength and a desperation for genuine affection and freedom, which surfaces through her secret relationship.

A key relationship that defines her character arc is with the ambitious and blind swordsman, Seigen Irako. While she is betrothed to Seigen by Kogan’s arrangement, she finds herself drawn to him, though their connection is fraught with peril as it constitutes an act of betrayal against the volatile Kogan. This affair directly motivates a significant portion of the story's conflict, as Kogan discovers the transgression and arranges a brutal punishment. In a moment of profound desperation within Kogan's bedroom, Iku contemplates murdering her master with a hairpin, revealing a flicker of violent agency born from her unbearable situation.

Her backstory reveals a formative experience of shared trauma with Seigen. In a flashback, the two are tied to a tree and left to die in the snow, where they are saved from attacking wolves by the swordsman Tsukioka Yukinosuke. This event forges a bond between them, as they find shelter together in a mountain village where Iku helps the newly blinded Seigen come to terms with his disability. This memory underscores the tragic nature of their later entanglement and Iku's role as a source of solace.

Throughout the narrative, Iku is positioned as a victim of the brutal samurai code and the cruel whims of the men who control her world. Her motivations are not driven by political ambition or martial pride but by a fundamental human desire for love and escape from a life of cruelty and social ostracism. She has no notable martial abilities or combat skills, as her significance lies entirely in her emotional and relational impact on the swordsmen. Her development is one of tragic awakening, moving from resigned acceptance of her fate to a desperate, though ultimately doomed, attempt to seize control of her own destiny.