Focus on things that you know cannot be easily obtained in Japan, Earl Grey tea goes very nicely. Do not get American chocolates for they won't be anything special unless they are from Belgium or the UK. Cuddly toys will also do nicely depending on the person, but ultimately, you should focus on luxury tea, biscuits, and things like that which won't break the bank and clearly is more unique from the country you are from. Don't bother with things such as clothes, leave that to your third visit when you are closer to your new friends as you will understand them more. Also, be prepare to take them out at least once when you meet up again in Japan and, in return, they will do their utmost to treat you well such as letting you see deeper Japan from the residents eyes. That will help you massively. Heh, everyone wins... New friends, unique pressies, new experience, new forever. Enjoy!