Valteishia, also called Waruteishīa, declares herself "Valteishia of the Sun and Solitude." She commands the Absolute Angel Megingjord and has endured multiple cycles of death and reincarnation, now residing within her fourth incarnation. Her existence stems from a catastrophe where the original Absolute Angel Cielo shattered into four entities; Megingjord itself fractured into separate body and spirit components. Valteishia embodies the spirit aspect, while Kū Shiratori constitutes the physical vessel. This division left both feeling incomplete, with Valteishia longing to reunite with Kū and restore their original wholeness.

Following the separation and lacking a physical form, Valteishia's spirit was placed into an artificial Steel Angel body by Kazuya Ayanokōji. This act resulted in her current form, making her the sole Absolute Angel inhabiting a Steel Angel construct. She serves as Kazuya's loyal companion and follower, executing his commands with little protest. Her actions under his direction include suppressing Kū's memories of Kyoshiro and immobilizing characters like Setsuna to enable their capture. Despite her compliance, Valteishia sometimes expresses remorse for these deeds and her role in Kazuya's schemes.

Valteishia possesses a distinct appearance: long, wavy blonde hair reaching her lower legs, a winged hat typically resting on her head, and amethyst eyes. Her attire usually consists of a long black, green, and white dress covering her body and pooling around her feet, complementing her pale complexion.

Her relationship with Kazuya is complex. She acts as his devoted protector and caretaker, continuing her assistance even after he suffers mental damage and becomes wheelchair-bound. While her loyalty remains steadfast, she harbors reservations about his methods, especially concerning other Absolute Angels. Valteishia also shares a profound connection with Kū, recognizing her as her other half. She expresses a deep yearning to reunite but respects Kū's wish to remain separate individuals, accepting this decision without force.

During Kazuya's attempt to fuse the fragmented Absolute Angels back into Cielo, Valteishia explains their origins and separation to Kū. She participates in the fusion process, which culminates in Cielo's reformation. Kū ultimately rejects the fusion to preserve the individual identities and loves of the separated Angels, leading to her bodily disintegration and reincarnation. Following these events, Valteishia remains alongside Kazuya, providing care for him in his diminished state.