Interesting comment, but I don't think you should ask this question or say yes to this question.

If you are the one asking this question: People usually feel put off when they are singled out for one specific aspect of themselves, especially if that aspect is something they have no control over, like being foreign. If they are foreign and already living in Japan this question has probably been told to them multiple times and they are most likely tired of/angry at hearing it. So you will probably get a no or rejection from them.

If you are the one being asked this question: Consider this, A (insert race/ethnicity) person you don't really know asks you "Let's be friends because I want (insert other race/ethnicity) friends!"
Would you be his/her friend?

If someone wants you for a specific physical trait of yours then they have already made assumptions about you and expect you to act a certain way. If you don't act like this, they will most likely stop being your "friend". Also it is harder to become real friends and fit in when someone wants you for one thing only.

If I have time, I would have a chat and see where it goes.

I think it's a little weird to ask people to be friends, it happens gradually and after that there's no need to ask anymore. I'd probably not say yes or no, but feel it's nice of them to show an interest in getting to know me.If I have time, I would have a chat and see where it goes.

This is a topic that is discussed fequently by expats and others living in Japan.

Personally, I agree with everyone else. You can't become friends immediately. Of course you'll have to start by getting to know each other and then seeing if you have interest in common.

I would be their friend.

I have many Japanese friends around the world. And I wish I could live in Japan. But, that probably will not happen.

Roy

If we have similar interests and get along pretty well, then yes of course! 

Getting new friends is always good! So yeah, if we're compatible then there's no reason why we shouldn't be friends.