In Tenchi in Tokyo, Washu was a renegade scientist who had helped Ryoko steal the Jurai Light Stone, an artifact of the planet, and was pursued by the Juraian forces (led by Ayeka) and the Galaxy Police (led by Mihoshi and Kiyone). During the chase, Washu sensed an unusual energy source emitting from Earth, and after they were forced to crash-land on Earth, Washu sensed that the power came from Tenchi's necklace (an heirloom handed down from his late mother, Achika Masaki).
Throughout the series, while researching his necklace, Washu invented various items that would allow the girls to see Tenchi during his time in Tokyo (notably, a dimensional portal), however, her inventions would often malfunction. Personality-wise, she's still a mad scientist, but she is more mellowed-out than her Tenchi Universe incarnation. When Yugi's plot had scattered the Masaki family, Washu was the only one not fooled by it and locked herself in her lab-closet to research. And after analyzing Yugi from her previous attack against the Masaki shrine, Washu found out she came from Jurai. With some help from Ayeka, Washu discovered the ruins to which Ayeka had been previously with Tenchi were actually a prison meant to hold Yugi, as she had been imprisoned for nearly destroying Jurai 3,500 years ago. Washu later sent an analysis robot to analyze Tenchi's girlfriend, Sakuya Kumashiro, as she suspected that Sakuya might be some factor in Yugi's plan, which proved to be true when the scan showed that Sakuya was a shadow of Yugi.
With her Gem Analysis complete, Washu went with Katsuhito to Tokyo, and she explained everything to Tenchi about Yugi and why she worked so hard to break them up. After that, Washu observed the final battle against Yugi, when she was transported to Yugi's dimension and at the end of the series went to work on a new Dimensional Tunnel by using the power of the gems.