Mnemosyne: Mnemosyne no Musume-tachi is one huge euphemism for sexual attraction.

The theme is something like supernatural detective and a little bit of action. But the real plot is the emotional journey of the main heroines, who struggle with a unique supernatural affliction.

I suspect the original idea was to illustrate how gender relationship are transcendental and beautiful. I feel the authors didn't quite succeed. To me it all felt a little too grotesque.