Kiriko is a childhood friend of the main protagonist Seina Yamada, and would often be tending to the many injuries that Seina would suffer from his bad luck. She cares for Seina deeply and would fight to protect him from further harm. Even her younger brother Kai Masaki would help out Seina in repairing (or otherwise constructing from new) the bicycles that would be wrecked because of Seina’s bad luck.
A secret from the wider world is that Kiriko, like all members of the Masaki family, is a distant member of Juraian Royalty, a descendant of First Prince Yosho, known on Earth as Katsuhito Masaki (Tenchi Masaki's Grandfather), and his wife Kasumi. Masaki children are not normally told of their alien heritage until they come of age but in the second GXP novel it is explained that Kiriko learned about her Juraian heritage earlier than usual by accident as a child. She overheard a visiting Minaho discussing a biological weapon released on Earth by space pirates, a symbiote that attaches itself to a host and passes onto new hosts, killing the previous one. Convinced Seina's bad luck would attract such a monster she rushes to his house to protect him. In an attempt to save him she struggles with the symbiote and it attaches itself to her, infecting and painfully mutating her arm, taunting her from inside her head. Minaho arrives and completely severs Kiriko's arm, apparently killing it. But she ponders how she occasionally still hears her regrown arm speak to her. This may partially explain her later bouts of uncontrollable rage.
After graduating from school, Kiriko went into the GP Academy, becoming an officer. She would only return to visit her family once every few months. From comments made, Kiriko had a very distinguished career. It once has being said that by a GXP captain and former mentor of hers, that if she wanted to, she could be the captain of a ship herself. She would merely need to make the request.
It is mentioned in the novels that Kiriko stayed in an area of accelerated time for ten years during her training.
For a time because of her familial status, Kiriko was one of the ladies-in-waiting of Seto Kamiki Jurai, the infamous "Devil Princess of Jurai." That connection helped Kiriko to gain a position with the Galaxy Police's immigration department, where she worked when she wasn’t on Earth.
Relationship with Seina Yamada
Kiriko is deeply in love with Seina, although she wouldn't admit it early in the series. Having grown up with Seina, she tried to convince everyone (including herself) that she loved him like a brother, though this was not true.
She met Seina through her brother Kai, who befriended Seina when the two first went to school. Kai's Jurain ancestry was suggested as helping them deal with Seina's bad luck. Being older, Kiriko would look after her brother and Seina. Even taking baths with them (a common practice in Japan, to make sure the younger children wouldn't hurt themselves in the bath.) A major turning point in their relationship seemed to be when, at some point, Seina's parents met Kiriko and Kai's, and his mother broke down about the fact that she was so happy that Seina actually had friends whom his bad luck had not driven away. It then became Kiriko's mission to help and protect Seina.
In the light novels, it is revealed that, while Kiriko does deeply care for Seina, she eventually left Earth in part to escape his bad luck, something which she felt deeply ashamed about.
It was while Kiriko was working in the G.P.'s immigration department that she found out that Seina had enrolled in the Galaxy Police. Immediately, she pleaded to the boy to return to Earth, without success. Soon afterward, she was assigned to the G.P. Academy, along with 2nd class Detective Amane Kaunaq, who is responsible for bringing Seina into space. During Seina's training, she had moved into Amane's house at the Academy along with Erma, although it was more to keep an eye on Amane and keep her from making a move on Seina. It was later on in the series that Kiriko began to feel inadequate compared to the other women in Seina's life – The supermodel Amane, noble space pirate Ryoko Balta, and more recently, high priestess Neju Na Melmas. It was after an experiment using Seto's ship Mikagami that her life would be changed. In a ceremony witnessed by Seto's husband Utsutsumi and Juraian Emperor Azusa, Kiriko was bonded to a second-generation Royal Tree, thus giving her the name Kiriko Masaki Jurai. The tree's name is Mizuki, and now aids the cabbit Fuku in powering the Kamidake II, the ship she commands with Seina and Amane.
Like Amane, Ryoko, and Neju, Kiriko was overjoyed to be engaged to wed Seina in a political marriage. However, before the ceremony could begin, Seto's ladies-in-waiting, who were actually agents of the Renza Federation seeking to use Seina's abilities to rid their home from marauding pirates, kidnapped Seina into their small ship and began to do sexual things to him in a public broadcast to ensure their non-Galactic Union organization's survival. As a result, the four are apparently included in the marriage, or at least the crew of the Kamidake II.
It is mentioned in the novels that because of the interruption, the wedding wasn't completed, so the groups are not (as of yet) officially married.
In OVA 5, it is mentioned that Kiriko joined an adventurer's guild in the Renza Federation, although the novels have yet to cover this time period, so details are missing.
As a G.P. officer, Kiriko has access to much of the G.P.'s standard complement of weapons and training in their use, as well as her Jurai strength. In one episode, she demonstrated the use of one of these – a bodysuit that featured cloaking technology, which enabled her to attack with complete surprise. Also in the heat of battle, Kiriko tends to concentrate solely on the battle and not on the environment around her – which was why when she approached Tarant Shank – covered in the blood of her previous opponents - she became surprised to find that Seina had seen her.
- The name Kiriko means "fog, mist, haze" (霧) (kiri) and "love" (恋) (ko).
- Kiriko's surname Masaki means "right, proper" (正) (masa) and "tree, wood" (木) (ki).
- The official GXP novels reveal that Kai and Kiriko are half-siblings with different fathers:
- Kiriko's father was a member of the Galaxy Police.
- Kai's father, Dai, is suggested to be a member of the Tennan family, making Kai a relative of Seiryo's.
- Kiriko and her mother were at the funeral for Tenchi's mother, Kiyone, although only half of Tsukiko's face was shown.
- A doujinshi, possibly a "what if" scenario, reveals that Kiriko and Seina will have a son who eventually marries Ayeka and Ryoko's daughters with Tenchi.
- Kiriko has repair nanites of equivalent advancement to Seiryo's.
- In the GXP novels, when Amane returned to modeling, Erma and Ryoko, as well as the Seto Scouts, joined as amateurs.
- In the GXP novels, Kiriko becomes owner of a powerful mecha that Washu built, originally intended for Kenshi, when he traveled to Geminar in the future.
- Rea didn't want Kenshi to find things too easy, so she forced Washu to not give it to him, so Kiriko ended up with it.
- Kiriko was once called a Demon Instructor. No real specifics have been given, either in the anime or the GXP novels, regarding how she gained this nickname.
- However, it has been suggested that she spent time at the Academy as an instructor before, or was often put in charge of new graduates to whip them into shape.