Tsunami is not someone who is easy to describe. Tsunami was originally one of three goddesses who were sisters, the other two being Washu and Tokimi. However, she no longer is a goddess, but she is still extremely powerful. She is the 0th-generation Juraian tree, the "mother" of all of the Trees of Jurai, including Yousho's 1st-generation Funaho and Aeka's 2nd-generation Ryu-oh. Being a Tree of Jurai, she also is her own ship of the same name as herself. However, she also appears in human form at times, and this will be explained more in depth. Tsunami is definitely one of the most complex people to really understand among Tenchi's friends. As it was stated before, no one knows when Tsunami gave up her goddess status to become the first of the Trees of Jurai. She is the source of Jurai's ships power, and it is from her and her "offspring", the Trees, that the Juraians are able to obtain their Life Water which enables all of them to live such long lives. The Juraian royal family's spaceships (Trees that are 2nd-generation or higher) are able to create the Light Hawk Wings, a very powerful energy defense with limited offensive capability because of Tsunami. The Light Hawk Wings take a tremendous amount of energy to create, with each successive wing that's created taking 10 times more energy than it took to create the previous one. The more powerful Trees of Jurai are able to create three Light Hawk Wings. Even Tenchi, who possesses the ability to create a Light Hawk Wing, could produce a maximum of three Light Hawk Wings. Tsunami, however, possesses the ability to create ten Light Hawk Wings! This is also not the full extent of the powers of Tsunami.
For as long as the Juraians could remember, Tsunami as a tree has dwelled at the bottom of the Juraian Tree nursery within the Royal Palace of Jurai. However, a little more than 700 years ago from the present, Ryouko, under the influence of Kagato, attacked Jurai with the purpose of capturing Tsunami for Kagato who wanted the power of Tsunami for himself. Ryouko failed to locate Tsunami, but during the attack Sasami, who was about three at the time of the attack, wandered into the room where the Trees of Jurai were kept. Amazed by the sight, Sasami began to explore and interact with the Trees. However, a damaged Juraian ship crashed into the palace, and the shock knocked Sasami from a ledge, causing her to fall a long way to what was supposed to be her death. She survived the fall, but she was very close to death. The place she landed at was close of where Tsunami was, and in order to save the Princess's life, Tsunami assimilated with Sasami. In doing so, Tsunami acquired a human form, that of Sasami at the age of eighteen (presently, Sasami is still only eight). By assimilating with Sasami, Tsunami and Sasami will one day become one being though at the moment they are two separate individuals. When they do become one, though, Sasami and Tsunami will still retain their individual memories.
Tsunami was very instrumental in helping Tenchi and his friends defeat Kagato. It was Tsunami who rescued Tenchi and healed him after he had nearly been killed when Kagato destroyed the bridge of the Ryu-oh. Tsunami also prevented Kagato's energy blast from destroying Earth by absorbing the blast with her Light Hawk Wings. It was also Tsunami that gave Tenchi the advice and encouragement that in the end enabled Tenchi to find the power within himself to defeat Kagato.
Although one of the most powerful people among Tenchi's family and friends, she is also one of the most gentle. She also has a wisdom that can only result through her experiences throughout the milennia. She does show a human side that makes her approachable and easier to relate to, as Tenchi found out when he first met Tsunami. Tsunami seems to care for Tenchi's family and friends and seems to look out for them, especially Tenchi himself, though for what exact reason it is not known.