The most notable/used UTAUs are Sora and Kyatto, making them the key people in the group. Although Akira and Mizuki are planned to be used sometime soon.
The MAHOULoids are an UTAU Group currently consisting of 4 released voicebanks: Sora Aine, Kyatto Yorune, Mizuki Nekone, and Akira Mahoune. The group name derives from the creator's name (Nagix Seuhiris, both names deriving from the word magic).
The first-ever addition to the group was Sora, initially just an UTAU OC concept but later made into an actual, released UTAU, voiced by Nagix Seuhiris.
He was then followed by Kyatto, also voiced by Nagix Seuhiris, and was given 2 additional voicebanks (CHARM and CHANT) soon after. A VCV was then made for her. Her concept was initially a vague cat named ASTRID but later on discarded. She was then revived as Kyatto the following year.
The third addition, Mizuki, is based on Nagix's pet cat, hence "Nekone" ("cat-sound") and her high-pitched voice. Also voiced by Nagix Seuhiris.
The, currently, last addition is Akira, voiced by pinkritualknife. She was a collab between pinkritualknife and Nagix Seuhiris with the design and personality.