Anime
In the anime, Princess Kakyuu came to Earth to look for the legendary Light of Hope, in the hope it would be able to save the galaxy. In order to protect herself from being discovered by Sailor Galaxia, she hid inside an incense burner, which was found and protected by Chibi Chibi. The Sailor Starlights, disguised as the Three Lights, performed their music to reach out and find their Princess, but she remained in hiding for some time as she tried to secretly discover the location of the Light of Hope.
Princess Kakyuu finally revealed herself in order to save Usagi from the black hole released by Sailor Tin Nyanko, at which time she asked for the help of the Solar System Senshi in searching for the Light of Hope. Sailor Moon wanted to help, but the others were suspicious of the strange Sailor Senshi. Before they could overcome their differences, Sailor Galaxia attacked, and Princess Kakyuu was killed defending the Sailor Starlights.
After Sailor Moon freed Sailor Galaxia, everything was restored, and Princess Kakyuu and her companions returned to Kinmoku.
Manga
In the manga, Princess Kakyuu came to Earth to search for Sailor Moon, the legendary soldier she thought could help save the galaxy. Because she was severely wounded in the battle against Shadow Galactica on her home planet, she needed time to heal after arriving on Earth. Chibi Chibi found her lying unconscious in a playground and kept her safe inside an incense burner while she healed her body.
The Sailor Starlights, disguised as the Three Lights, performed their music to reach out and find their Princess. When Seiya drew a connection between the incense burner and the scent of their Princess, the three tried to take the incense burner from Chibi Chibi. Kakyuu then emerged and explained why she had been missing for so long. She then indicated that Chibi Chibi was actually a Sailor Senshi.
After a brief battle with Sailor Tin Nyanko, Princess Kakyuu explained Shadow Galactica to Usagi. She also told Usagi that Sailor Galaxia’s final target was Sailor Moon. Usagi decided that she must go fight as a result of this, and Princess Kakyuu guided her to the center of the galaxy, Sagittarius Alpha Star.
As they reached the center of Sagittarius Alpha Star, the Sagittarius Zero Star, they encounter Lethe who sends Kakyuu and the others into the River of Lost Memories. Eternal Sailor Moon is able to overcome the effects of the River and revives the rest of the group. Just as Eternal Sailor Moon was about to emotionally connect and reach out to Lethe, Sailor Chi and Sailor Phi kills both Lethe and Mnemosyne. Chi and Phi are at this point able to overcome Sailor Star Fighter, Healer, and Maker, stealing their Sailor Crystals as well. Thrilled with their victory, they momentarily retreat back to Galaxia to present her with the Sailor Crystals they have taken.
Kakyuu breaks down but is encouraged by Eternal Sailor Moon to continue on in hopes of rescuing everyone’s sailor crystals. Kakyuu, Moon and Chibi Chibi arrive in an area covered in thick fog which is revealed to be the final resting place of dead stars. Sailor Heavy Metal Papillon greets the group and vows that she will make beautiful graves for them as well, she then summons vines to pull the girls down into empty graves. As all hope seems lost, Sailor Chibi Moon and the Amazon Quartet arrive from the future to help save the present. Chibi Moon is able to free Kakyuu and Eternal Sailor Moon with her attack while the Amazon Quartet’s combined attack vanquish Sailor Heavy Metal Papillon. After Chibi Moon explains the effects of Galaxia’s actions on the past, the team regroups and continues onward.
They soon reach the Star Garden where Sailor Chi and Phi are awaiting them. Kakyuu demands that they return the stolen Sailor Crystals of the fallen soldiers and reveal that she too, is a Sailor Soldier, transforming into Sailor Kakyuu / Sailor Kinmoku. A battle ensues and Kakyuu displays her abilities, she is able to keep Sailor Phi busy and with Kakyuu’s guidance, Eternal Sailor Moon is able to defeat her. In a blind rage, Sailor Chi impales Kakyuu from behind killing her. As Kakyuu bleed to death, she wishes for a world of peace without struggles, and says that she was glad to have fought alongside Sailor Moon. A reanimated Sailor Venus then steals Kakyuu’s sailor crystal and tells Eternal Sailor Moon that her new opponents are none other than her own fallen, reanimated allies.
It is uncertain of Kakyuu’s fate at the end of Sailor Moon, though it is presumed that all the sailor crystals were reborn at the ending.
Although Kakyuu never displayed Soldier abilities in the anime, in the manga she was able to transform and recite attacks. Her transformation is “Kinmoku Star Power Make Up” and her attacks are “Starlights Royal Straight Flush” and “Kinmoku Fusion Tempest”.