Visiting bf who is in millitary

My boyfriend will be stationed in Japan from next month, obviously I would like to visit him, I'm going to do that in three months time, then I need to go back to US, for at least 2months, but ASAP I want to get back to Japan ( even 2 months apart it's a tragedy for us :( ) my question is: how is it with entering Japan? can I go back and forth as many times as I want? Should he prepare me some invitation or something? I heard about some people who were not letting go through on Narita airport? Is it common in Japan?
any advice will help

Assuming you are American, it is very easy to enter Japan on a tourist visa. You don't need to do anything beforehand except have a valid passport. Once in Japan you will get a temporary visitor's visa allowing you to stay for 90 days. Now it shouldn't be a problem to leave and come back (especially with a 2 month stay outside of Japan), however if you do that too many times in a year then immigration may become suspicious (the general estimate being that spending more than 180 days/year in Japan as a tourist looks suspicious). This is more of a concern to people who max out their 90 day tourist visas and only taking shorts trips out of Japan to get new tourist visas though, so your plan may not raise as many flags with immigration. Just be aware that you could potentially be denied entry if it looks like you are trying to live in Japan on a tourist visa.

thank you very much for an answer :) so I can visit him twice a year? doesn't sound good to me.

Hey Miley
Have you thought of getting a civilian job on the American base? You could get yourself a SOFA visa on your own, and then you can stay as long as you keep that job.

As mentioned, the first time you probably won't get asked questions, the second time you might get asked lots of questions, trying it a third time and you might be in trouble. But everyone's experience is different, for example you might get questioned on the second try and get a 15 day permit instead of 90 days.

Your options are:
1. Get married
2. If you have a university degree, find some job in Japan and get a work visa to live and work in japan
3. No degree, become a student and live in Japan.
4. get a job working on the military base (not japanese government related).