Hmm, well, you might just be making a really bad choice of date. If you pick a date that she's really not in the mood for and that also doesn't suit your skills, it is possible to get a negative result from the date.
I could see that happening once or twice while I figure out the system, but I have been matching the dates to her moods and still getting the negative results. The same approach works fine for the other ladies, just not for Nobuko.
I take that back. Apparently I was screwing up the dates. I went back and did it a couple of times more and finally figured out what I was doing wrong. Now I have it. Thanks for the response and for the fun game.