In the US asking may be fine.
In Japan F it may be seen as intrusive. I wouldn't even ask the other pax or FA's.
BTW, there are 2 reasons not to be concerned with sitting together:
1.. Conversing is extremely difficult, even with the the barrier down. (I sat in these 2 seats with my nephew once)
2. Conversation would not be appreciated by the other pax in the cabin.. The seats are designed for relative privacy and comfort; not for socializing.
BTW, JL (as well as NH) F is pretty nice. Enjoy your trip!