D Sanada began as an alien refugee whose civilization escaped to Earth carrying the core robot Zinv, pursued by the malevolent entity Kumu and the robot Himiko. Her faction rejected technology while rival groups embraced it, sparking conflict that destroyed her original biological body. Preserving herself within Zinv's suspended animation, she was later discovered inside an alien artifact in a parallel world. Earth Defense Force scientists transferred her astral essence into successive artificial bioroid bodies. The fourth stable vessel housed her astral self within her left eye socket, manifesting as a glowing orb usually hidden by her bangs. This form expressed limited emotion and social comprehension, speaking mechanically and interacting minimally except with protagonist Kazuki Yotsuga, who uniquely engaged her.

Living with Kazuki and others, she gradually developed human emotions and attachments, particularly toward him. During the final battle against the Rara Army and Himiko, she overcame her deep fear of robots to sacrifice her bioroid body by crashing into the enemy ship. This act enabled Kazuki to awaken Zinv's full power and revealed her preserved original biological form within the robot. Returning to this body, she removed Zinv's power limiter. After the merger of parallel worlds created a unified reality, she was adopted into the Sanada family as Dee Sanada, displaying a cheerful and expressive personality contrasting her earlier reserve.

Billions of years later within the expanded Tenchi Muyo! GXP continuity, her enduring astral pattern remained within Zinv on a desolate planet. Found by Seina Yamada (Kazuki's reincarnation), her consciousness was transferred into a bio-engineered cabbit-hybrid body modeled after Fuku. This form retained visual elements of her bioroid appearance, including the glowing astral eye, despite her capacity for emotional expression. Joining Seina's interstellar crew, she operated the Kamidake II spaceship and became one of his spouses, echoing her bond with Kazuki. The Tenchi Muyo! OVA series notes her astral pattern's resemblance to Neju Na Melmas, indicating a deeper cosmological link within the franchise. Her favorite food is curry.