Interesting short story. It was thought provoking in a way. Maybe its an interpretation of a time when drug trafficking was on the rise in Japan. the little boy could be a representation of people straying from a good path (cram school) and getting lost. Another possible interpretation is corruption and the loss of innocence. The beautiful woman could represent a form of temptation or persuasion. Note that she was jovial and playful at first. Lowering the audiences guard. She could also represent the decline of an individual addicted to drugs. The two where frolicking happily until the mater of the white bag came back up.
But maybe i'm reading too much into it or i may be missing information based in the dates given. If so, it was still a good story and I still like it quite a bit.