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This is more how a Japanese man would do nampa, very obvious, false pretexts, followed by random targeting. It is a numbers game, but it is also not one. This much low-grade, random nampa will burn you out in weeks, not to mention grind down the "cool factor" of Westerners.
Needless to say, one of the greatest advaneforum.xxxes of a foreigner in Japan is the better game we were forced to develop in our Anglo countries. I've had Japanese girlfriends tell me about the weak nampa of Japanese guys: one mentioned being approached by a stranger who, in a sheepish way asked her for coffee because his friend never showed up, another was just flashed (not uncommon in Japan). Often most Japanese men just discreetly molest as a form of nampa (I don't want to most Japanese men do this. There are many honest, generous j-men).
I've nampa shita on the streets with Japanese women who didn't know English successfully, but this isn't usual. The language barrier will always get you before other stuff does.
The "I'm lost" works good, especially if it is in the evening and the destination is an English bar/coffee house. Also, if you see a girl reading English material (English is popular in Japan, though no one actually can speak) ask if she is studying. Otherwise, I would scope out the girl, see if she has an attitude, eye contact and make a comment on clothes, prodigious cell phone texting and go from there. The conversation does not have to be clever, just pleasant. If the girl knows no English, I am relegated to my very poor Japanese skills. The only topics are: job, food, where I am from, my stay in Japan etc. In addition to hand signals, one might wedge a future date into that. If she knows a little English, just be normal. In fact, complex jokes and slang will not get past the language barrier.
Almost all Japanese girls are polite enough to talk, even if not interested. Many girls are not approached in Japan believe it or not, so they will find you talking to them pleasant. The problem again is the language barrier.
I have enough Japanese to push for a date and talk about my job. That is almost never enough. However, some girls will go for the "lessons" angle, though you are fighting an uphill battle from there because lessons often mean just that. The Japanese woman has not developed the B.S. meter that Anglo women have because Japanese men don't have to invent them. I suppose an electronic dictionary would help. Garnering numbers is not a complete wast either. The chance of a Japanese woman going home the some day with a man, especially out of a club environment is very small.
It is actually hard for Japanese women to meet foreigners, even if they know English, so if you are an average decent guy, you are already ahead of most non-Anglo guys with this woman.
However, because there are so few English speakers, expect rejection. Ozgaijin's numbers are way off. You could pick up more women by flashing in Japan. I will give him credit for trying at his age and with poor Japanese skills.
I would also disagree that most j-girls don't want a foreigner. Though they don't think about it in those terms, the combination of hollywood and gaijin's greater masculinity, chivalry and game puts all westerners a step up from what they would be at home. I have never met one guy that couldn't hook up in Japan that wasn't trying, this includes a fat, smelly Euro-grad student, an ugly, fat disagreeable man and an Englishman who insisted on wearing tuxes everywhere and had a dark, quiet brooding about him. There are also many more pretty women in Japan then we are accustomed too.
The reason why there aren't many top-notch j-girls with westerners has more to do with the former's lack of English and the fact that there is a lot of physiological homology in Japan, for instance I have only seen a nine in Japan seven times in my 1.5 years there, while I've heard that other Caucasion countries have very many. I've actually heard old Japan hands mention how they miss the toads back home because they get board with the high-quality, yet standard j-girl model, it be a rough 7 back home.
A big city is also necessary because the women will shun you if they know you are double dipping and everybody watches the lone gaijin, everybody. There are also very few women in the provinces, almost all in the city.
Again, it comes to the language barrier: a guy in his twenties that isn't a complete troll, but has excellent j-skills, will be almost as cool as Bond. A tall, above average twenty-something, but with almost no Japanese skills (myself) will have to try hard: go out on the weekends, do the occasional nampa when the target looks right, use internet dating as a supplement, but he will clean up. After a few months in country, I find myself having too many girls to spend time with in addition to job, napping (English teacher hours are all early weekend) and keeping track of names (you must always vet new talent to keep the cycle going, as most girls fail). Needless to say, I've never been in Japan long enough to get out of the "prisoner-on-leave" phase most Anglosphere men enter when they travel abroad.
Guys out of their early thirties with j-skills can still do better then non-speakers in their twenties, but the thirty-something without language skills will be in more trouble. If he works an ekaiwa (language school) job, he may want to try a different country. He could still have a very good time in Japan, but it may not be worth the lost income, harassment at work etc.
One might also be aware that not all English jobs are equal. When I did JET I had loads of time, couldn't be fired, higher pay and a network of other JETs and more respect from locals, as I was a government employee. My second time as an ekaiwa instructor, I was forced to do their boring lessons, had to project the genki dork of a j-salesmen (watch how fast the students will complain on you the slightest form slip up), horrible schedule that gave me only a few hours sleep a day if I wanted to go out on weekends, loopholes that sucked my paycheck etc.