oh man, i really hope, this is just some "first love"-thing and the author is baiting us.
the story up to this point is insane good and now potentially putting incest after 400+ chapter would be such a wrong move in so many ways...
but i still bet that she is not Ameri's mom, because she does not look like her mom in the flashbacks we had.
EDIT: Since it seems people dont understand my comment and i try my best to be respectful.
please read my comment fully. I wrote a very important word and that is "potentially", that implies this is just a theory!
EDIT 2: Guys, to have a nice discussion, you need to really read a comment and try to understand the intent.
media literacy is such a important skill
EDIT 3: this will be my last edit, since i am tired...
Firstly people just assume the maybe-incest-route, because Japan is known, that they are not as strict in this topic like other countries.
Secondly i don't want that route too!