Dark Washu began her life as the "Dark Crystal", a device which Washū Hakubi created approximately 5,000 years prior to the events of Tenchi Muyō! Ryō-Ohki. The Dark Crystal was a self-evolving artificial intelligence program with the rather unusual purpose of attacking its own creator by any means it could devise, in order to provide a worthy opponent to test the "perfect" security system that Washū was attempting to create. When Washū was sealed away by Kagato, the Dark Crystal had not yet been activated. However, it was discovered by Washū's jealous colleague Doctor Clay, who subverted the system to pursue his own grudge against her. When his attempt to abduct Washū on behalf of Tokimi was thwarted, just before being delivered to a Galaxy Police prison, he activated the Dark Crystal with orders to kill Washū. Shortly after its activation, the Dark Crystal reconfigured itself into an android copy of Washū, except with dark skin, purple eyes, and pale purple hair. This gave her most if not all of Washū's superhuman powers, theoretically allowing for an even contest. She also claimed that her personality was a copy of Washū's.
Rather than attempting to attack Washū in secret, "Dark Washu" (as it called itself) instead openly announced her presence and intent. She followed this up almost immediately by attempting to kill Washū with a garrote, and then with a hand-held energy cannon. After being physically assaulted by Ryōko for the second attack (which if successful would have killed Tenchi as well), Dark Washū concluded that a continuation of direct attacks would soon destroy the Earth, and instead proposed a best of five competition between herself (and four duplicates) and Washū's "team", with the type of contest in each round being randomly determined. The first round, a cooking contest, was easily won by Sasami, but Dark Washu cheated to defeat Ayeka and Ryōko in a shōjo manga trivia contest and a foot race, respectively. Mihoshi tied the competition in a contest of drawing lots, leading to the final round: hand to hand combat between Washū and Dark Washū. Dark Washū used deceptive tactics, such wearing boxing gloves to present the impression of a boxing match and then using kicks, but was still defeated by her creator. She then conceded defeat and exposed a shut-off switch to Washū.
However, at this point an orbital satellite left behind by Doctor Clay fired on Washū, and while it was proptly destroyed by Ryōko, the satellite placed a more sinister personality, a copy of Clay contained within his removed left eye, in control of Dark Washū's body. Clay told Washū that he would continue attacking the entire Masaki household unless she would erase their memories and confront Dark Washū alone on Europa. Though Washū obeyed this demand, Minagi arrived on Earth shortly afterward and was able to get Tenchi, Ryōko, and Mihoshi to remember Washū's existence. They arrived on Europa just in time to prevent Dark Washū from inflicting a killing blow. Afterward, Dark Washū's true personality was able to reassert itself, weakening Clay's hold, and Washū defeated her with a German suplex. Clay's copy attempted to retaliate with a proton bomb, but Washū had already disarmed it. Minagi then destroyed Clay's eye, eliminating the copy forever. When Washū expressed reluctance to deactivate Dark Washū, the android grabbed her hand and forced her to do so.
Following Dark Washū's defeat, Washū repaired and reprogrammed her as Tama (玉?) to serve as a lab assistant. Tama appeared to be a smaller, more child-like version of Dark Washū and wore a red and white maid's outfit. When questioned as to why she had restored the former villain, Washū responded that "cute characters don't grow on trees", implying that this was done largely on a whim. This was supported by the fact that she installed a very powerful self-destruct device in Tama-chan because "it seemed amusing".
Tama-chan generally got along well with the other members of the Masaki household, but behaved antagonistically toward Ryōko, seeming to mimic Ryōko's own behavior toward Ayeka. Ryōko challenged Tama-chan to a fight, with the loser being required to leave forever. However, Tama's self-destruct device was accidentally activated, causing her to forfeit the fight and flee into deep space. Upon realizing the reason for Tama's actions, Ryōko pursued her and sliced Tama-chan in half, leaving behind her lower body (which contained the bomb) and bringing back her head and upper body to be repaired by Washū. Though Ryōko was still annoyed by Tama's attempts to steal her food, she no longer objected to the girl's presence. Tama-chan has since played a minimal role in the story.