In the world of Sword Gai: The Animation, Kei is a woman defined by an extraordinary and enduring love. Her entire existence revolves around her devotion to Seiya Ichijo, a powerful fighter whose body is in a state of suspended animation, preventing him from aging. Kei, however, has not been granted the same timelessness. She is a woman of advanced age, likely in her seventies, who has spent decades living alone, faithfully and patiently waiting for Seiya's rare visits.

Kei's most defining characteristic is her profound and unwavering dedication to Seiya. Her love transcends time, loneliness, and the physical effects of aging. She is a gentle and seemingly delicate woman, but this exterior masks a remarkable inner strength and a courageous acceptance of her unusual fate. A significant part her personality is rooted in a poignant psychological coping mechanism. Unable to reconcile her own aged appearance with the unchanging youth of her beloved, Kei lives much of her life believing she is still a young woman in her twenties. She sustains this illusion by frequently imagining Seiya's presence, sharing her daily life with a version of him conjured from her memories. This fantasy is her primary comfort and the lens through she views her solitary existence. However, she is not entirely lost in delusion; she is subtly aware of the growing gap between her reality and her memories, and when Seiya does occasionally appear in person, she sometimes questions whether he, too, is simply a figment of her imagination.

Kei's role in the story is that of a tragic, grounding figure, representing the human cost of the supernatural conflicts that surround characters like Seiya and the protagonist, Gai. She serves as a poignant connection to Seiya's past and his humanity. Her key relationships are almost entirely centered on Seiya Ichijo. She is identified explicitly as his lover, and their bond is the core of her narrative. Theirs is a love story marked by prolonged, painful separation, as they can only meet when Seiya is not called upon for his duties. Kei's devotion is so absolute that she has structured her entire world around these fleeting reunions and the memories of their time together.

Throughout the series, Kei's personal journey is one of quiet decline and peaceful resolution. She suffers from a heart condition related to her age, and despite a care manager's suggestion that she be hospitalized, she refuses, preferring to spend her remaining days in the home filled with her memories of Seiya. She seems to sense that her death is approaching. In her final significant action, Kei insists on having one last date with Seiya. During this outing, she experiences a severe heart episode. Using her last remaining strength, she presents him with a treasured wedding dress and receives a marriage proposal from him, fulfilling a lifelong wish. In her final moments, she asks if she has wasted her life by waiting so long, but she ultimately reassures Seiya with a smile, declaring that she would never want a life without him. She then passes away quietly, at peace with her choices.

While Kei does not engage in combat like other characters, her notable abilities are not physical but emotional and psychological. Her primary strength lies in her capacity for absolute devotion and selfless love. Her most significant power is her unwavering faithfulness, which persists despite overwhelming loneliness and the passage of time. She demonstrates the ability to shape her own reality through her beliefs, a delusion that is both her greatest vulnerability and the source of her resilience. Her story leaves a lasting impression of steadfast devotion and the bittersweet beauty of enduring love, even when that love is defined by loss and longing.