Need effective flirting in japan/japanese

So I've spent enough years in japan to get to know the ropes here. But there's always room for improvement and I'm always learning new things. It may be a long shot, but if anyone has experience in japan with Japanese girls, I want to hear what works in the flirting/seduction phases for you guys.

Most Japanese girls won't respond to a pretty overt invitation to sex. It's more effective to have the sex unspoken, only implied or as a mutually assumed alterier motive. Might seem weird, but there are much weirder things happening in this country.

Sometimes a simple invitation to go out with my friends and I or on our own for coffee can totally change a girl's attitude and she doesn't return texts anymore. It doesn't happen all the time and I'm meeting people so often that the ones who fall through the cracks don't matter so much. But I've become more selective over the years and if a girl I really want to see again responds negatively to me or something I said, that's a lost opportunity and I want to minimize these from now on.

So if anyone has any tips or advice (especially if you've lived or currently live in japan), it would be greatly appreciated!

I can speak Japanese pretty well, so if you have anything to add in Japanese too, feel free! Looking forward to any insightful replies!