What if...
View attachment 2292885
What if...
What if Ami thinks she's not related to Sensei is because she found evidence in her mom's things that suggest Sekai was cheating and her daughter was a product of that affair
BUT she doesn't know the affair was with Sensei... so she
thinks that they're unrelated when actually they're even
more related? Like a diary where Sekai talks about the affair and wrote about how she's certain her baby is from the other man as her husband didn't have sex with her around the time she was ovulating or something, like she knows it's the other man that fathered it without a doubt... and this way if/when Ami reveals the fact and shows the diary to Akira, then
that's the moment he realises Ami is his daughter? Like, that moment would have to be after Sensei becomes self aware of his affair with Sekai again but it'd work wouldn't it?
A diary of secrets of her dead mother's would explain a lot of Ami's supposed meta knowledge and it'd be the sort of thing that'd make such a person cocky with said secret knowledge. It'd also be exactly the kind of thing Ami might find digging through he parents things looking for mementos and heirlooms to treasure and connect with her dead parents.