Outside vs. Inside
The reality is that most women here who like foreign men do so simply for the reason that they are foreign men. It’s considered very cool to go out with foreign men; foreign men are considered very “kakkoi”, and many women are attracted to them for this reason. The first thing therefore that you have to be careful of is not becoming somebody’s plaything or status symbol. Many women who you meet who take an immediate liking are more interested and excited by what you are, rather than who you are.
You could be her boytoy, her cool gaijin boyfriend; she’ll show you off to all around her. She doesn’t really care what you have to say, and doesn’t really care about you. You’re almost a fashion accessory. These sorts of relationships tend not to last all that long. If you’re fine with the arrangement then go for it, but if you’re looking for something more serious (whether consciously or unconsciously), be careful not to get too attached to somebody who doesn’t care about you quite as deeply as she may make out.
Many, many men fall into this trap, and it’s sad to see them hurt.
Likewise, try not to get big-headed. A lot of foreign men start to believe that they are special, just because they are superficially treated as such. You may be treated like some sort of celebrity, but do try to remember that you’re not one. People’s excitement and interest in you is not as deep as it may appear.
I don’t wish to sound too melancholy. Of course feel free to go and have fun. There is no doubt lots of fun to be had. All I’m saying is that you should be aware that it often looks like a Japanese girl cares about you more than she truly does, so if you feel yourself becoming more attached, just keep your feet on the ground, and keep everything in mind, or it’s easy to get hurt.
All the best.