Hien and Souhi are Hinoto's two servants. They're identical twins who took on the task of caring for Hinoto after their parents (also Hinoto's sevants) passed away. Out of respect for Hinoto (and because it's what their parents did), Hien and Souhi refer to Hinoto as Ohime-sama or princess. The two are fiercely protective of Hinoto, and quite willing to violently punish disrespectful "infidels" such as Kamui and Sorata.
The kanji for their names can be read as follows : [Hien = blue ice] [Souhi = red flame].
The CLAMP Campus Trio is another series crossover in the X series. The original series they're from is the "CLAMP Campus Detective Team", shoujo manga. In that manga series, the three were elementary school children. In X, they've all grown up and are now the Board of Directors for the CLAMP Campus. The trio make their first appearance in book eight, when Tokiko requests they protect the second Holy Sword. The CLAMP Campus was built in a star shape expressly for this purpose. Afterwards, the trio appears sporadically throughout the rest of books 8&9. Their true purpose is yet unknown. The Trio consists of (above picture left to right) Suoh Takamura, Nokoru Imonoyama and Akira Ijuin
Daisuke is the nephew of Aoki Seiichiro, and is another wind master. He makes his first appearance spying on Kamui with Arashi in book one. He watches as Kamui is accosted by shikigami (spirit beasts) in the form of men. Kamui obliterates the shikigami, tearing up the surrounding area in the process. Because of Kamui's apparent disregard for other people, and his choice not to set up a kekkai before fighting, Daisuke refuses to believe that Kamui is Kamui. Later, Kamui and Daisuke fight, each seriously injuring the other. Kamui is about to kill Daisuke when Arashi appears and rescues him. Later still, Daisuke and Kamui once again face off. This time, in Hinoto's secret chambers under the Diet Building. Aside from his avid dislike of Kamui, Daisuke is fiercely protective of Hinoto, and would lay down his life for her.
