Helena von Bähbem is the niece of Ernst von Bähbem. A childhood acquaintance of Makoto Isshiki and Itsuki Kisaragi, she serves as the second in command in the Bähbem Foundation. In addition to being a childhood dabbler in witchcraft, she was a potential instrumentalist, but passed the ideal age without realizing her potential. This makes her jealous of Quon and others that might succeed in tuning the world
Elvy Hadhiyat is an ace pilot for TERRA, and participated in the operation to extract Ayato from Tokyo Jupiter in episode 1, and is the leader of TERRAs Alpha Squadron whom all pilot futuristic fighter craft and backup the Rahxephon in battle. She is from Indonesia and is Haruka's drinking buddy. (Source: Wikipedia)
Maya Kamina is Ayato's mother and is often away from home, leaving Ayato feeling neglected and wishing to spend more time with her. Although Ayato initially believes she works in a lab, she is actually a very powerful Mulian leader. Just before Ayato leaves Tokyo Jupiter for the first time, Maya is injured by flying debris, and Ayato is severely rattled when he sees her blue blood. From then on, he is fearful and mistrusting of her.
Mamoru Torigai is another friend and classmate of Kamina's in Tokyo Jupiter. He was seeing Hiroko Asahina before she left Tokyo Jupiter with Ayato. Deep down, he dislikes Ayato because of Asahina's feelings for him. Mamoru is a true Mulian, like Ernst von Bähbem, Maya, and Quon, and holds a high position within the Mulian society
She can't speak and can't play piano good.
Quon Kisaragi is a mysterious young girl who speaks the first words of the TV series and is shown meeting Ayato in episode 4. Her standard expression of surprise or agreement is "Ra-ra" (or "La-la") and most of her dialogue is cryptic and musically themed. She and Ayato do not connect romantically, but she displays a level of both physical and interpersonal comfort and intimacy with Ayato that is unmatched by any of the other characters, even Haruka. She is also one of the few people who never treats Ayato as a curiosity or an annoyance, and she seems to have an understanding of his situation and what his eventual role is, calling him Ollin ("motion" in Nahuatl). Like Ayato, she has the marks of a potential instrumentalist. She and Ayato are both shown undergoing examinations, and while outside of her home she wears a vest-like device called a Life Module. Quon is skilled in playing both the violin and piano. She also is portrayed as curious about music that other people listen to on headphones, often taking them off to listen to the music.
Itsuki was raised in the Bahbem Institute with Makoto Isshiki and Helena Bahbem, and is the adoptive brother of Quon to whom he is very attached to. He is the leading researcher of the RahXephon and Dolems and studies their relationship with music. He once dated Haruka and is aware of the special connection between her and Ayato. He once tried to pilot the Rahxephon at Makoto's urging only to have the water surrounding it slam him against a wall, taking the form of Reika afterwards. For that he is highly envious of Ayato.