Really curious if Ruriko is going to end up being a bad person or not. If we're following in the steps of I Can't Say No to the Lonely Girl, she'll be a comically bad person that nobody likes. Though I honestly do kind of doubt that approach.
I have a feeling she's going to be someone who assumes what she wants is what everyone wants. She took Miyuki away presumably because she thought that doing a bunch of music and singing stuff to become the best singer possible is what Miyuki wanted, when in reality that is likely just her pushing her own dreams on to her child. She likely also assumed that Yuu wouldn't have been as hurt by it and would be supportive and want the best for her sister, likely because she couldn't see all the negative effects because she views this as exclusively positive.
Honestly, thinking about it, I might have to retract the statement on Ruriko's mom not following in the footsteps of Sora's Mom, because I accidentally just described what is basically a nicer version of Sora's Mom. Because Sora's Mom also thought what she was doing was what Sora wanted, and only realized it wasn't when Sora spoke up. So Ruriko might be Kashikaze making a better version of Sora's Mom.
Could be wrong on all of this, by-the-by. I ain't Kashikaze, I just think it's fun to analyze a story and see where it might go. Ruriko could end up being the most evil and malicious character I've ever read and I'll facepalm at this comment in a year, but, on the flipside, if I'm right I'll feel like a God.