Valteishia, referring to herself as "Valteishia of the Sun and Solitude," commands the Absolute Angel Megingjord. She has experienced death and reincarnation many times and is now using her fourth body. Valteishia is the current companion of Kazuya and his loyal follower. At Kazuya's command, she apparently suppresses Kū's memories of her time with Kyoshiro and stuns Setsuna so he can take her away. Also, Valteishia likes Kazuya.
When Valteishia explains how the original Absolute Angel Cielo was split into four beings, she clarifies that one of those further subdivided into its body and spirit. Kū is the body of that one Absolute Angel, while Valteishia is its spirit. Lacking a body of its own, this spirit was shunted into a Steel Angel body by Kazuya and became the current Valteishia. Valteishia apparently longs to be restored to her 'vessel', Kū, although she seems to regret some of Kazuya's acts and her own part in them. After the series, she aids a wheelchair-bound Kazuya, who appears to suffer from some mental damage.
Her design is adapted from Valkyrie, of the anime and manga series UFO Princess Valkyrie.