If you read on Sasami's profile page, you know about Sasami and Tsunami being one person. Tsunami is a tree spaceship, (if you don't know anything you just thought...'a tree can be a spaceship and take human form?...'quoting Ryoyo. ^_^) and is one of strongest in the universe. Compared to Tenchi's sword and powers, Tsunami and Tenchi's powers are equaled. (good they are on the same team!) Because Tsunami's powers are deep within Sasami, whenever there's trouble Sasami usually has a dream before it happens warning her.

In one episode of the Tenchi series, Sasami reveals her story about her and Tsunami. Tsunami explains that now Tsunami and Sasami have separate Minds, but when Sasami grows up she will have one complete memory (their minds will combine). When Sasami and tsunami are shown separate Tsunami is only a hologram, because Tsunami isn't a separate person, she's Sasami's older self and protector. Tsunami explains in this episode that when Sasami grows up she will look like Tsunami and they will be one together, you can then call her Tsunami or Sasami.

Kind of Confusing? Just remember that they are the same person, that's all.