I find it interesting, because seriously (as much as a manga can) exploring the mother/daughter incest idea is rarely seen and on an intellectual level, the implications are mind-boggling.
Of course, were it to be something happening in reality it'd be really disturbing.
Yeah, people sometimes complain about the use of tropes in stories, but basically stories are always built on tropes—tropes used straight, inverted, avoided, transformed, whatever. The “schoolgirl yuri” genre has a fair number of elements (if it were a board game you’d call them ‘counters’ or ‘pieces’), and they get deployed and combined in a variety of mostly familiar ways.
But as you say, this particular variation isn’t seen very often, especially not developed at any length. If these stories were handbooks for social behavior, this situation would be pretty problematic. But I’m pretty sure we don’t need a Fictional characters on closed course. Do not attempt at home
warning tag.
Hope so, anyway.