A doctor with TERRA, he is also the adopted brother of Quon. Although most people do not know, he is actually a Mulian and Ayato's twin brother, and his adoptive "sister's" biological son. Like Megumi, he feels inferior to his sibling. He is unable to pilot the RahXephon and he once dated Haruka, but Haruka now rejects him. He was raised in the Bahbem Institute with Makoto Isshiki and Helena Bahbem. Like Ayato and Quon, he bears the marks of a potential instrumentalist on his belly.
(Wikipedia)
Kisaragi Itsuki is TERRA's top researcher and a purported expert not only on the RahXephon, but also on the absolute barrier of Tokyo Jupiter and on the technology which TERRA uses to create Vermillion. He is Kuon's older brother, at least they live as such, though Itsuki's true feelings for Kuon are deep, and ambiguous. Itsuki is also Ayato's younger brother, and he was at one time involved with Haruka. He was raised as a potential instrumentalist by the Bahbem Foundation, along with Isshiki Makoto and Helena Bahbem, who later muscle in on TERRA and Itsuki's research. He is also cold to his assistant, who is hopelessly in love with him.