Recruited by Captain Kirk to join the Enterprise crew immediately before the Khitomer Conflict broke out. Hikaru was not pleased to have his sister in the crew.
Working in Engineeringm Kirk recruited her away from the crew of the Armstrong because she is the highest rated technician in Starfleet. Yuki was also at the top of her class at the Academy. Her talents are immediately apparent to Hikaru's best friend, Pavel Chekov.
As the Khitomer Conflict unfolded, it is reveled that Yuki is an agent of Section 31. Her Starfleet Academy roommate had been killed in the destruction of Vulcan. Yuki's grief and desire for revenge made her susceptible to recruitment into the shadow group. She departed the Enterprise in the company of Section 31 agents after nearly destroying the Klingon homeworld at the climax of the conflict.