If you're going to be here several times in the next 4 years, that sounds like very short-term adventures. So, you really shouldn't expect to make any close friends anyway. Japanese people are rather hard to get close to, also. Friendly on the outside, but not close until you have built up a relationship.
If you are going to visit schools, be aware that most college-age Japanese may have gone through 6 years of English education in JHS and HS, but it didn't focus on conversation. As a result, that and their innate shyness and fear of making mistakes will mean you will have to initiate lots of conversation. Learn some Japanese and don't be afraid of making mistakes, because many Japanese figure we foreigners can't learn it anyway.