Seeu's past is a very tragic one. His mother was supposedly very weak (physically) and died from giving birth to him. His father died early on as well, and Seeu was raised by dolls. From the time he was born, he was never touched by another human being. This is because he lived inside a palace that had a veil draped over the entire building which acted as a force field. Nothing could get in, and nothing could get out. The veil was kept active because there was a bacteria on the planet Asu which could infect a person in fifteen minutes. The disease was fatal and incurable, and the people reasoned that if Seeu was never exposed to the air outside the palace, and he never came into direct contact with them, he would survive long enough to find a way to save them.

Seeu was admittedly not accustomed to humans, and always seemed blank and emotionless (one character comments that he was "unfamiliar with the workings of the human heart"), but he cared for his people and worked hard to find a way to preserve their lives. Through 3D images and conversations through the veil, he worked with the scientists on the planet to try and find a way to transfer a human soul into a doll's body. With this procedure, he hoped to transfer all the people into bodies that would not be affected by the bacteria.

Sadly, Seeu was not able to succeed before the people of Asu died out. Not long after that, the planet Asu exploded and was reduced to a collection of rocks drifting in space. How that happened is unexplained. Apparently Seeu was able to get through the veil by using the Luna Mercury, one of the legendary living weapons. The Luna Mercury is supposed to grant eternal life to its master, and Seeu is obviously the one it chose to wield it.

Somewhere along the way, Seeu met Kagami, who we are told does not belong to any of the worlds, and is the owner of another living weapon, the Organic Gold. How they met is unknown, but they became close and fought together in a war 300 years ago (in which Kagami seemingly died). Sometime after that, Seeu began making dolls in Kagami's likeness. His best doll so far is Gold, who even wields the Organic Gold weapon and looks identical to Kagami in every way.