The last few chapters have been rather revalatory. In fact there's almost too much information to absorb here. So here's an interpretive recap:
-The mother Ayuko seems to be suffering from a mild to moderate form of dissociative disease called Emotional Detachment Disorder (EDD). Her normal reaction to other person's emotions is to put up a fortress wall of aloofness and eliminating any trace of empathy. She can disguise it through smarmy politeness and a modicum of kindness to, but she treats everyone like they were a passing acquaintance or a customer. She has very few friends and no lovers beyond her late husband.
-This aloofness extended to her daughter Asuka. Her inability to form emotional attachments and show affection made their relationship unstable, and instilled great anxiety in Asuka, whose deepest fear is one of maternal abandonment. Ever since she entered grade school, Asuka has worked tirelessly to try and win Ayuko's approval, including academic over achievement, hypochondria, and mild to moderate self harm. But the only thing that has aroused her mother has been appealing to her suppressed kinks and perversions.
-There is a heavy subtext of past and present sexual abuse. Disassociative disorder is usually due to abuse, and Ayuko displays other red flags as well. There are problematic statements: "All the crimes I've committed" in the monologue at the beginning of chapter 5, or telling Asuka that it's "probably my fault" for her daughter's incestuous desires. And a highly codependent relationship anyway. Given that her mother is a pharmacist, with access to sedatives and depressants (including insomnia drugs whose side effects include short term memory loss, and were popular with Japanese rapists a few years ago), and demonstrates dodgy professional ethics, there is the strong suggestion that Ayuko has been clandestinely abusing Asuka, and the latter only has a few fragmented memories to inform her.
In summary: this is a deliberate train wreck of a manga full of damaged individuals. And I haven't even touched the secondary characters.
