The exact known time of when the Ostinato Musicians were founded is unknown, but they were established when Thorn, the group's leader, suggested to μ that she should make a group that would both protect her and compose songs for her whilst also acting as her own personal task force. μ agreed with this idea and chose six individuals from Mobius, each of whom was aware of Mobius' nature. Unlike the members of the Go-Home Club, they do not wish to return to the real world for various reasons, namely in part for μ promising to grant their utmost wish.
In truth, the Ostinato Musicians were meant to be used as tools by Thorn by filling μ with negative energy through their concert performances, which would make her more compliant to her wish to destroy reality.
- Thorn: The leader and founder of the Ostinato Musicians. As the leader of the group, she is the most dedicated to ensuring the Go-Home Club does not interfere with their agenda. μ trusts her explicitly and listens to whatever she says. She also bears a strong grudge against Shogo Satake.
- Sweet-P: A premier fashion icon who creates delicate, feminine-sounding music. She also has her very own fan group known as the Flower Princesses.
- Kagi-P/Kensuke Hibiki: A former member of the Ostinato Musicians, following his defeat at the hands of the Go-Home Club.
- Shonen-Doll: A hooded young man who lives in Mobius' library, composing rather gloomy and depressing songs. He abhors the idea of companionship and despises anyone who leads a social life.
- Mirei: An immensely popular member who lives in luxury at the Sea Paraiso. She has many male followers and seems to have a one-sided rivalry with μ, though the latter is completely unaware of this.
- Ike-P: Izuru Minezawa's classmate, who is very narcissistic. He is popular with the female student body and enjoys showing off to further his own ego.
- Shadow Knife: μ's personal bodyguard and enforcer. He is tasked with hunting down traitors in Mobius under the guise of "justice." His appearance and mannerisms appear to be based on an anime character from the past.
- Wicked: A mysterious member of the musicians. Their gender is a mystery and no one knows much about them. They write violent, but impactful and deep songs.
- Lucid: The newest member of the Ostinato Musicians. They serve as the double agent of the Musicians, spying on the Go-Home Club.
- Kuchinashi: One of the Ostinato's more listless-looking members. She is one of the more social people of the group and surprisingly easy to talk to, and uses a special device to synthesize a voice rather than using her natural one.
- Stork: A good-natured Musician who's songs are very popular with the women of Mobius. However, due to his perverted tendencies, he is met with very little respect.
- A few members serve as foils to members of the Go-Home Club:
- Mirei and Kotono. Both can be considered the most beautiful members of their respective groups, but whereas Kotono is very gentle and kind, the former is cruel and selfish.
- Izuru and Ike-P. Izuru couldn't care less about his so-called popularity and Ike-P revels in the attention he receives.
- Kotaro and Shadow Knife. The latter is more extreme and targeted the people who bullied him in real life, wheras Kotaro resolved to fight his bullies head-on without fear.
- The protagonist and Lucid, ironically enough. Lucid betrays the group after gaining their trust for being unable to maintain a resolve to return to the real world because of their trauma, whereas the protagonist stands by them and having the resolve to face their trauma.