I have no clue if this was addressed in the manga, but the whole plot had a glaring flaw for me. How come Minami was not able to kill Yuki because she was "too powerful", while Midori was able to do it VERY easily, with no apparent consequences? Minami knew that Yuki was the killer, if she wanted she could just take a gun and shoot her in the house, there, problem solved. I don't understand why she had to die, it makes no sense at all. You could argue that Nanaka didn't do anything because she underestimated Yuki or whatever, but you cannot say the same for Minami. This was the biggest flaw I had with this show.