Sakuya Kumashiro has been rated 3 on Temangu High's "Must Have List" by her male classmates. However, it is newcomer Tenchi Masaki that gets her attention. On one of his first days, she chooses to sit next to him at lunch, much to the envy of the other guys. Over the course of the series, the two become closer, culminating in the school carnival, where the two share a kiss while Ryoko is watching, causing Ryoko to run away for much of the series' remaining episodes.
Sakuya has strong feelings for Tenchi, and, in the end, her love becomes so strong that she can't bear to be without him. This only gets stronger when Sakuya has a great realization near the end of the series. Yugi keeps a close eye on her, and Sakuya seems to be involved in her plans.
Sakuya goes through a big change when, in a later episode, Tenchi realizes that Sakuya has never spoken about her home, her parents, or anything about her past. Sakuya brushes off the question like always, but this time she becomes aware of the fact that she can't remember anything about herself. In her life, all that has mattered is Tenchi, and she hasn't thought of any of it.
Sakuya begins breaking down, and clings to Tenchi even tighter. The two spend a great deal of time together, and Sakuya tells Tenchi she loves him, asking him if he loves her. He is unable to answer for the time being, and wants longer to think about it.
He doesn't get much time, though. Yugi, who has been watching her, keeps saying that she doesn't understand her. The little child can't comprehend the romantic feelings of the older girl, and the actions it causes. Yugi destroys the crystal in her inner sanctum that represents Sakuya, and Tenchi finds that his school friends have no idea who she is. Tenchi runs off in search of her, but cannot find a trace that she had ever existed.
Tenchi returns home, and receives a phone call from Sakuya, who has been walking in the city, feeling empty and alone. The two spend the day together in the beach, sharing a kiss there, and Tenchi returns home to find Washu Hakubi and his grandfather Katsuhito Masaki waiting for him. They explain that Washu has made a discovery about Sakuya: she is another persona of Yugi, a shadow or reflection of her as a young woman that she created (although her actions and Yugi's confusion by them shows that Sakuya has a mind of her own). Tenchi refuses to believe it at first, but after Washu shows him her data which is a definitive proof, he runs to Sakuya's house. When he makes it there, he finds Yugi, who had moments before taken Sakuya back into herself after revealing the truth to her.
When Tenchi confronts Yugi, Yugi places him in a dream world, where he can be with Sakuya forever. Distraught upon the loss of Sakuya and his guilt upon confronting the other girls after their fight at the carnival, Tenchi goes along with this after the Sakuya of this world, which is supposedly nothing but Yugi's puppet, speaks to him alternately with Yugi's voice and then her own, and he finds himself unable to hurt Sakuya.
The two share some time together, and Tenchi finally gives Sakuya the answer to the question she'd asked earlier: taking her into her arms, he tells her that he's thought about it, and realized that he loves her too. They kiss, but this makes Sakuya breaks free of Yugi's control, and she tells Tenchi that he has to go back to the real world and save everyone. Then, Sakuya says she'll never be alone anymore since Tenchi gave her memories to hold on to, so she willingly fades away into nothingness and sets him free so that he can restore everything to the way it once was.
- Ryoko once hypothesized in the end of the series that, since Sakuya is Yugi's shadow, the now-sleeping Yugi might grow up to be Sakuya when she wakes up. However, some fans have hypothesized that she wouldn't grow into Sakuya, but could use her powers to bring Sakuya back instead. If either of these does happen, it will certainly make the competition for Tenchi's heart that much more heated.