I know I'm probably alone in this thought but.. I don't really like Miki all that much. Like, I know the author is trying to make her appear to be helping Yuizaki in her own way, and she clearly needs a bit of a push since she's quite timid and indecisive about all this. But.. as Yuizaki said, she is enjoying this way too much, and it really comes across that she is using her sister's relationship with this guy for entertainment. Which is just never ok in my book.
In my opinion, while she is useful as a plot device, she's not a very likable character.