huh... what made him flee niki and them as a teenager then for noriko to find him later in his 20s to be her tutor?
Based off what I can remember:
Sensei didn't ghost and dump Niki until after the car accident when he lost Sekai and was presumably 23 (hence all the 23's that tend to show up and there being 23 layers of hell.), This was after dating Niki for 5 years, so when he was presumably in college she was in highschool (hence her mentioning no one believing she was dating an older guy). After the accident, he took in Ami, and Niki fell into depression, let her parents know Sensei was tutoring, then they set up Noriko to be tutored by him. This is also when he tutors Maya. He's a tutor until he's around 28 or 29/almost 3 years before the game starts, then he disappears completely from the Nakayama's, for unexplained reasons, moves with Ami, and becomes an actual Teacher. Then comes the space war, him teaching the class, Yumi detentions, and the timeloop/gods stuff apparently.
In other words, his first disappearance was more of a "not coming around anymore after a tragedy" thing. They still had contact with him. It wasn't until almost 3 years before the game starts that he disappears on Noriko completely, which she thinks was because of Maya.
