Maya Fey, also known as Mayoi Ayasato in the Japanese version, is a spirit medium who is training in the Kurain Channeling Technique. This allows her to communicate with spirits of the deceased and give them temporary control of her body. She is also Phoenix Wright's assistant for three years, tagging along with him during investigations and helping him solve the mysteries of the cases. Maya has long black hair tied up in a bun. She also has a purple jacket and a lilac colored robe. Around her neck is a necklace made of pearls and a brown magatama on the front.

Maya's first appearance is in the original Ace Attorney game. She is framed for the murder of her sister, Mia Fey, and Phoenix is tasked with defending her. After the case is a success, she joins him and works at his office, the Wright and Co. Law Offices. Although she was initially devastated by the death of her sister and being accused of killing her, she recovers to her usual joyful self after the case is closed. In every case after, she can be seen messing around with Phoenix, making witty jokes and being distracted by childish things. Often she'll be craving hamburgers more than she wants to work on the case. But when the situation gets dire, she does pull through, helping Phoenix put together the pieces of the case or calling on the spirit of her sister to aid him.

In the second game, Ace Attorney: Justice For All, Maya makes a return to the series, but she becomes yet another suspect in another murder case. She gives Phoenix her magatama and instructs him to meet her little cousin, Pearl. The magatama becomes key in solving the case because it allows Phoenix to see people's Psyche Locks. Breaking these Psyche Locks by presenting the right evidence pressures witnesses to reveal information they had initially sealed away in their hearts. Maya is once again proven innocent thanks to the help of Pearl and the magatama. In another case in the game, she is kidnapped by one of the murderers and is not found until the end of the trial.

Maya plays a large role in the final case of the third game, Trials and Tribulations. Phoenix and co visit a temple in the mountains that is known to be spiritual. During an overnight stay, Maya becomes trapped in a small temple on the other side of a bridge, along with another spirit medium. Maya is attacked but somehow her attacker is killed. She doesn't help Phoenix with this last case because she is thought to be trapped in the temple, but it's later revealed that she was channeling someone during the entire duration of the case.

Maya makes minor appearances in later games, including Ace Attorney Investigations. She is also Phoenix's partner in the Phoenix Wright vs Professor Layton game. She does not make an appearance when Apollo Justice is the main character, though Phoenix sometimes mentions her in passing. She makes a return in Ace Attorney: Spirit of Justice.