OP - don't be afraid to travel there. I also take 'gifts' for those I know, the worst problem I've encountered is endless marriage proposals & demands for my phone number (know it back to front now!)
I think now that the picture is a little clearer, you could go over with a little 'something' as it's an exchange; maybe keep it hidden away until the end of your stay ... or when you think is appropriate.
Enjoy the trip, Japan is safe, lived there 3 years but I love Africa too & see no reason to put off this trip!
Kira
