thank you my dear Ho Ching for the recommendation. It was a relatively smooth read for me, the twists and turns were interesting, but it felt expected coming to the end...
(potential spoilers below, ft. my personal summary of the book)
This story talks about a family who's mother is afraid of the daughter diluting the fathers love - so she starts to talk, to act, and finally, believe she is her own daughter. The father seems like a lunatic as well for not being able to tell that that's his wife, and even playing the role of a doctor and talk to himself. There is also a character, portraying a stalker1 who is madly in love with the mother, and believing that everything she does is out of love for him.
Apparently, the real 'Mayouri' shows only at the later half of the story, saying that her mom has been faking her identity all along. She demonstrates the hatred she has towards her parents, whom are supposed to love their child. Mayouri collaborates with the stalker to kill her dad. But in the end, she seems to go cuckoo not being able to tell herself from her own mother...