As a Japanese, I welcome you from the bottom of my heart and I adore your active youth to come over to this far east country by yourself.
All I can say from a little experience of working with foreigners, there is a distinctive difference among them. Though they spent a couple of years working in Japan, some learnt the language here and got many friends, and others were not able to speak nothing more than a few greetings or ‘survival Japanese’ for travellers and got terrible homesick. What makes this big difference? The answer: acceptance of differences. Those who enjoy staying here tried everything, even if it is a little peculiar to them. Food, events, parties, manners, … everything. Those who lead miserable staying seems to refuse the differences, they look down on some of our culture, never touch local foods, and complain a lot.So, try everything you will happen to encounter here. Eat it, swallow it, and taste it. Communicate each other, tell your frank feelings to people around you. Be a good friend of us. Good luck!