Just request assistance at the airport. And select the one that requires assistance all the way to the seat. That should be a fairly standard procedure, and should be requested in advance. As a standard, there are jet way in both JFK and HND, but of course exceptional cases can occur.
Selecting a seat in advance with AA codeshare is always a bit complicated. But if you get a note with your assistance that you require an aisle seat, I am fairly sure it will work out.