I wanna go to Japan for tourism purposes, but I don't have a guarantor for my letter of invitation for my visa?

Question:

I am US resident but hold Vietnamese passport and I plan to go to Japan this summer with a friend for tourism purposes. So I know I need visa, but since this is just tourism, i have no "guarantor" or anyone to write me a letter of invitation as they require from their visa procedure. What do I do? Will my visa be denied?
The thing is my friend has relatives in Japan and we might stay there during our stay. However, I'm not sure if they will agree to write me a letter of invitation cos they don't know me. Anyway, I wonder if anyone has gone through the same thing and can advise me...
Many thanks!!!

Answer:

You can only ask them and find out. They are under no obligation though if they don't (and don't want to) know you. Japan has had lots of 3rd would people go to Japan for illegal work and never leave, so they are quite strict now - even if a lot of their economy depends on it.