Psychologically our tendencies is to project our own ideals onto others subconsciously. What we like in others is what we "think" is the right kind of person. Most of the time we're looking for a partner who's as toxic and emotionally abandoning like our own mothers.
A friend of mine can't get enough of Japanese girls and won't date girls of other ethnicities. When I asked why, he mentioned that Japanese girls have "mysterious" personalities. Turns out it's the emotional abandonment type that he's drawn into. Some of my Japanese exes were like that, I was quick to discard them as soon as they show their sour side. Like some bros here have pointed, some J girls can disappear without saying goodbye because they're good at emotional abandonment. They don't initiate "breakups" just because it is their culture to be polite and not cause fights.
This J girl you mention, she's out with you mostly because she knows that you're harmless and won't take advantage of her. At the same time she feels lonely but doesn't want a relationship. Not many J girls are prepared to have relationships with non-Japanese men, the cultural differences are too wide and parents may not approve foreign partners. Also J girls are likely to settle with foreigners only if they are non-confrontational and good at keeping the harmony.
I had seen a Japanese WL outside of her work before, years ago. We went shopping together, had dinner and spent time at her home. We'd lie on the sofa together, hugging but no sex or kissing. She only allowed it during her work not on her day off. And she specifically told me we are not in a relationship - at least "not yet". All kinds of mixed messages came from her so I decided to stop seeing her one day, and told her that I'm only going to see her again if she agrees to make our relationship official. She tells me that she can't do both relationship and WL work at the same time so that's the end of us.
Funny thing you mentioned her giving you "more and more while paying less and less". If she works in a shop then it seems that she might be giving you diamond service at standard price or she's running her own private gig. Or this might be a fantasy fiction. Anyways, can't care less if this story is fiction or real because mine wasn't. And I wouldn't waste time chasing any girl's attention or pussy because how I met my current partner taught me a lot about relationships I missed out in the past few decades - if she likes you, she treats you very well, fucks you really good and says yes immediately after asking her to be your girlfriend - she's a keeper!
I've been dating too many time wasters and I should've known better in the past decades.