The second daughter of Empress Misaki Jurai, Sasami is the younger sister of princess Ayeka. During the fateful raid of planet Jurai by the space pirate Ryoko, she was involved in a terrible accident: falling into the great chamber containing Tsunami, the original and most powerful of the Juraian trees. The accident mortally wounded the young girl, but Tsunami wasn't about to let the princess die right in front of her. Instead, she fused her own spiritual body with Sasami's, effectively recreating Sasami and healing all her injuries.
Sasami remains largely unaware of this situation. She doesn't remember the accident or the fusion, and lives her life as if none of it happened. Tsunami has stated that eventually the two of them will fully merge until there is no difference between one and the other, though presumably this will not happen until Sasami ages (and given the Juraian lifespan, this could be a long, long time). Tsunami herself rarely ever makes her presence known, preferring to remain a silent partner in their relationship. Sasami is aware on some level of what happened to her and what she is, though she prefers not to think about it.
Sasami is a cheerful and precocious child. She is kind and humble and nice to small animals. She also has a slightly playful streak, and like most children likes to get into mischief. Tsunami, contrarily, is a very regal presence. Fully aware of her status as a Choujin, one of the supreme gods of the universe, she takes her current condition and responsibilities very seriously. She deeply cares for Sasami and for the people around Sasami, and is not above stepping in with all her powers if she feels she needs to.
Sasami is very young but still very powerful. She is a skilled at hand to hand combat and much stronger than she looks. She can easily take out well-trained and equipped soldiers by herself. As Tsunami, her powers are almost without limit. Tsunami is the first and most powerful of the Juraian trees and all the others are measured against her and found wanting. She can produce ten light hawk wings (three were sufficent to resist the force of a black hole), instantly teleport across space and communicate with any other Juraian tree in the universe. She can heal damage up to and including the loss of over half a person's body mass. If she decided to unlock all her power, she can strike with enough force that the shockwave would snuff out stars across a large swath of the galaxy.