With all that came out this update I estimate the timeline to be something like:
1)Akira is born and around 0~3 years draws the affection of his half-sister Sekai. (she is playing peekaboo with him)
2)He is around 12 and hurts his leg, Sekai offers to take care of him bringing the two together.
3)Akira and Niki get together too, probably when he is 13~14, when he is 15 Sekai gets pregnant and tries to take him to Kyoto.
4)Akira is 16, Ami is born in august, Noriko should already been born in july.
5)Two years later Niki is 16, brags about having an older boyfriend, Akira should be 18 and in colege.
6)Teacher course is around 4 years, Ami and Noriko should be 6 when Akira finishes colege.
7)Around a year after Akira finishes colege, he should be 23 and Ami is 7,Sekai dies in a car crash, Akira breaks up with Niki and boards the depresso expresso stuck in bed station, only enough of will left to get Ami from the orphanage.
8)Notices he should earn a living if he wants to feed himself and Ami, starts tutoring, finds Maya, and Noriko finds he is tutoring and convinces her parents to sign her.
9)Around 3 years later Maya works her magic to make him disappear from Noriko's life. Ami and Noriko should be around 10 now.
10)Sometime during the last 5 years he starts teaching in Kumon-mi High, and we reach the time of the start of the game where Ami is 15.
