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Person who owns a Dollfie Dream, here. I can answer some general questions if you're too lazy to go to /jp/. I don't really post there because I could never get into the community there. I've been owning DDs for like almost 10 years now.
Sadly I don't own a Miku, but I have Rin and Luka though and a handful of anime ones.
The Miku in question I think they just drew the smile wider as a joke and gave it smaller than usual eyes giving it a yandere effect or something.