As a fellow introvert, Ifm in awe of you going on a hostel-hopping holiday alone with the intention of meeting and actually talking to strangers. Go you! Japan certainly seems like a very good choice for this due to being generally safe and people being polite and helpful.
I was a bit less bold in my own vacation and went with friends, booking our own private room at hostels and such. Also, as westerners we didnft have any issues of some sort of negative prejudice towards Chinese or something.
Anyway, with regards to meeting people I do have some suggestions, depending on your budget and your own preferences.
1) The easiest is a suggestion I also made to someone else on this site: plan to meet with a volunteer guide from the university. It gives you someone to spend the day with and an immediate contact with a Japanese person. We started our trip in Kyoto and used
http://goodsamaritanclub.org/ to arrange a meeting with an university volunteer. There's also a link to a similar organisation in Nara on this website. I'd assume something similar exists for Tokyo as well.
2) Visit a (ryokan with) onsen: sitting naked in a bath with other people does seem to encourage conversationc If youfre bold enough to do that, at least (we picked Tsurunoyu onsen not only for the beautiful old ryokan and outdoor bath, but also because the water was emilkyf and after sort ofc sneaking over to the bath and carefully turning my back and removing my towel I could slip in with my prudish sensibilities mostly intact. Also, it was great!)
3) Pick an activity that encourages social interaction. With this I mean something like a workshop, maybe a tea ceremony, a cooking workshop, some sort of crafty-thing? (For example, we went to a stencil dying workshop in Kyoto,
http://marumasu.sakura.ne.jp/english/). Once again, these are just suggestions/examples, but itfs something you can consider. Itfs even more fun if you can find somewhere where there are usually not many foreign tourists.
Good luck with your planning, and have fun!