Hisui Diamond (ヒスイ・ダイヤモンド, Hisui Daiyamondo), or Princess Hisui (ヒスイ姫, Hisui-hime), is the main protagonist heroine of Ice Jeweler.
A Jeweler from Kobutsu, a planet in the Hoseki system, she is the daughter of King Saphiro and Queen Rubia, younger sister of Prince Toparz, and older sister of Second Princess Ameji. Like the Icejins of the Dragon Ball universe, the Jewelers have the same bodily features, even the tails, but are a bit more human- or Saiyan-like, give or take, and they have a gem on their foreheads; Hisui's gem is a jade, for which she is named after.
Anyways, getting back to Hisui, she is twelve years old, entering a stage of puberty. On the day of her birth, a young girl from planet Earth named C.C. came to Kobutsu and gifted her with a mysterious ability called "Geass". Saphiro and Rubia feared that she could lose control over it, so they made her forget about ever having it, forbidding her from using it.
On her twelfth birthday, Hisui made a wish that she would train some time away on Earth like Toparz did, ten years prior. With Jadeite, Nephlite, Zoycite and Malachite aiding her, she traveled to Earth on a space ship, where she befriended Fribbles Cold, the Jolt Icejin. After traveling with Fribbles to his High School, Calvin Q. Calculus High, Hisui gains the power of Ice (Koori). Afterwards, she started making new friends along her journeys, even fell in love with a monster (even though it's a forbidden love).
During her mission in Japan, her Geass power awakened after being confronted by Britannian soldiers. She begged (actually commanded) them not to shoot or kill anymore people, and they obeyed her without question, dropping their weapons. Soon after, her Geass power was discovered. Afterwards, one of her friends, JRuff (a veteran Torentuff), informed her to talk to someone named "Lelouch", and ask him about her Geass power.