Reiko Akanezawa can be recruited if Tamaki refuses to help Charlie and Yumi and meets Reiko two times at the Music Club - she will be in the room first after visiting the Nurse's Office, and next after collecting the equipment from the Storeroom and all 4 clubs.
On Reiko's path, a bit of Ideo Hazama's backstory is revealed. Reiko's path is an extended version of Yumi's path on which after beating Hazama you can enter his mind and beat him a second time, which unlocks the true ending of the game.
Reiko first appears in the battle against Akira Miyamoto, protecting Hazama. After stopping the battle, Reiko warns Hazama to not let his guard down, because someone wants him alive and gives him a love letter from another girl, though Hazama faints before reading it. Reiko is also seen in the temple connecting Karukozaka High School to the five worlds of the Expanse, and joins the party to defeat Zurvan, however, this only happens if Tamaki Uchida accepted the "Ring of Light" from Lucifer.
Reiko appears much differently than she does in the original game. She is a classmate of Nobu when he transfers following the incident at Karukozaka. While she initially is friendly with him, even trusting him after being framed for his mother's murder, she yells at him when she discovers he is responsible for her brother's death. She is responsible for Hazama's later reincarnation.