Maya apparently showed up after the accident, after he ghosted Niki, and shortly after he began tutoring Noriko again:
At least that's what Noriko's 'Loxosceles Reclusa' seems to say.
I don't think Sekai met a 6 to 7 year old Maya, and I'm not sure it's even jealousy that is Sekai's problem. She just seems to hate Maya, and I'm thinking it's likely because Maya convinced Sensei to forget Sekai, along with the Nakayama's. Could be wrong though.
The reason i think Sekai isn't jealous of Niki as she is of Maya, is maybe Sekai thought of Niki as an alibi girlfriend for Akira.
Made it easier for Sekai and Akira to hide their relationship.
There are also still some vague things.
Ami mentiones something like she was in an orphanage shortly after her parents died for a short while. Smth like: "Some creepy people tried to adopt me" iirc.
So where did Akira live during that time?
A place where he lived for a long time before the car crash?
Did he rent a new place?
What we know is, that after he took Ami in from the orphanage (if she was in one), they moved to her parents home.
We also know that he had a seperate place to tutor.
Either the turoring place was his old apartment or he rented it additionally.
If he rented it additionally, why did it need a bed? Bathroom maybe, but bed?
What i think is that before the car crash he already took Maya in. Either in his old apartment, which might also be the tutoring place, or he rented a seperate place for her.
Maya says she was living in an apartment, no mention of parents, like she lived alone.
Seems strange for an underage to live all on it's own without some supervision, and that role Akira might have filled.
Why does Noriko believe that Maya joined the tutoring after her?
Wouldn't be surprised if Akira send Maya away everytime he tutored at the beginning. Untill Maya was fed up with that situation and insisted to be part of the tutoring.
Sekai seems to have known about the Akira/Nikki relationship before her demise.
I guess Good Boy Akira told her. And Good Boy Akira might have told her about Maya.
Also, I don't think Sensei really ever got better per se. Even now, he gets to the point where Ami has to take care of him:
It seems more like he just has good days and bad days etc. Even around 8 to 9 years later.
Yeah i mean thats one of the major things going on, not?
He's a dysfuntional human being.
In the special case you're showing with the images though, might they be another example of how "manipulative" Ami uses her knowledge about trigger words to force him into the depicted state? Did she mentioned Sekai and or her death/car crash in that event?