Sensei's Sister-In-Law

Sensei's sister-in-law was the wife of his brother who died in the car accident. Sensei Prime appeared to be infatuated with her, complementing her perfume and upsetting his brother. She was Maya's mother in the real world.

Within Kumon-mi
Inside the simulated world of Kumon-mi, Sensei's sister-in-law is retconned to be Ami's mother. It is also implied that given the choice to resurrect one person, Sensei would choose "Ami's mom", although it's unclear if this is referring to his sister-in-law or Maya Prime.