Basically, even if you are typically perceived as a "zero" here, then you could very well be a "hero" there. I really hate to put it in these terms, but if you are confident then it is actually pretty easy. Now, it depends what you're looking for. If you're looking to get laid, then just like Buddha-rama said, go to Roppongi. Ikebukuro is kind of a hotspot, too. Basically same rules apply there--offer to buy them a drink and go from there.
However, if you are looking for a relationship, then just say, "hi. I am still friends with 5 of the women in those 6 relationships. That's pretty much it. The conversation should either take off from there, or you'll know if they think you're a Creeper McCreeperson, at which point you should just smile and drop it. Either way, whether you're looking for friendship or whatever you can get, neither the suit nor the facade as a Toyota employee is necessary.
Most Japanese girls aren't into casual sex so may be considered more 'conservative' than western girls. They may also have a lack of 'private places' to go to for 'romance' as Japanese are reluctant to invite people back to their homes, let alone a foreigner!
There are many 'love hotels' around the place, but most nice girls are reluctant to go there; especially in the evenings as they may have to catch the last train home.
Get the Lonely Planet guidebook on Japan as they'll have a section on what you want to know. Bon voyage! It really depends on a girl. There are some girls who want to communicate with foreigner, also some girls who doesn't want to do. Even the former, they are varied. Some are willing to have a boy friend who is foreigner and some are just interesting to have a communication or brush up their conversation skill in English.
