Princess Kakyuu (火球皇女,Kakyū Purinsesu) (commonly subtitled as Fireball Princess) is the princess of Kinmoku, a fictional planet outside of the Solar System She is said to smell like the flowers of the sweet osmanthus, which are a recurring motif in her character design. The name of her planet is a pun on the name of these fragrant blossoms, which are called kinmokusei in Japanese—the suffix sei, when added to Kinmoku, means "planet" or "star." When Kakyuu first introduces herself, she calls her specific kingdom Tankai, a homonym of another word which also means the Sweet Osmanthus shrub. Kinmoku is also the home of the Sailor Starlights, who are Kakyuu's protectors and spend much of the story searching for her. The details of their collective story vary between the manga and the anim
In the anime, no mention of battle-wounds is made, and her purpose in going to Earth is to find the "Light of Hope" and hide from Galaxia. During her time under Chibichibi's care, she is aware of the Sailor Starlights searching for her, but cannot reveal herself too soon. She finally emerges to save Sailor Moon and the others from a black hole and resumes leadership of the Starlights. The Starlights imply many times that, like Sailor Moon, Kakyuu has the power to restore a Phage to its original form. They claim that they have to kill them as that is all they can do with without her. This power is never shown. Not long after Kakyuu is found, Galaxia appears in battle and personally takes Princess Kakyuu's star seed. (Unlike the manga, Kakyuu never transforms into a Senshi form, although she is shown to have a "true star seed.") Kakyuu sets up a forcefield that is able to block Galaxia's attacks for a short time, but it does not save her. Before dying, Kakyuu sees in a vision that ChibiChibi herself is the Light of Hope. After Sailor Moon defeats Chaos, Princess Kakyuu is revived. She and her Starlights return to their home to rebuild and start over.
In the manga, Kinmoku is attacked and destroyed by Sailor Galaxia, leaving almost no survivors. Kakyuu herself travels to Earth and hides within a censer protected by a small child, ChibiChibi. Having lost contact with her, the Sailor Starlights follow behind, searching desperately. Kakyuu is injured in the battle with Galaxia, and cannot reveal herself until her wounds are healed. She travels to Earth because she senses the birth of the Silver Moon Crystal (which is an evolution of the original Silver Crystal). She is shown to have her own Senshi form, called Sailor Kakyuu, and reveals to Sailor Moon that her own lover had died in the war against Sailor Galaxia. Her uniform appears as a cross between her normal dress and the outfits worn by the Starlights, making it unique among all the Senshi. She eventually accompanies Sailor Moon to Zero Star Sagittarius to confront Galaxia, but is brutally killed by Sailor Chi. She dies in Sailor Moon's arms, saying that she wants to be reborn, maybe in a world without war, but at the very least to be with everyone again. Her body is then destroyed and her Sailor Crystal taken by a reanimated Sailor Venus, who has been revived along with the rest of the Sailor Team to serve Galaxia