@Xunder That's just kids not understanding how to come to grips with a reality like that. It's too far away for them to really feel it, but they also know they should feel something from it; just not what they should feel. So they revert to familiar mechanisms, such as gossiping, or find that they're repulsed by the situation.
yep she killed mii-tan coz she was in the way of sahara and her, then sahara coz she couldnt get a hold of him or something, hell looking at the last page she could have killed the cat too.
Is every chapter going to be ending with a creepy face? That's one hell of a way to remember the manga! @Hollow7F I have 3 theories for that. Just like you said maybe she killed Mi-tan out of jealousy and MC because she couldn't get a hold of him but that wouldn't explain her wanting to continue. or maybe she killed Mi-tan out of jealousy and found a liking to killing. I somehow have the feeling that she wants to keep her important and maybe cute people by her side and therefore kills them so that they stay by her.
Regarding the Ren-chan, I think that she wants to "have her" later and enjoy the moment for now or she might just want to avoid suspicion. There were other people there as well and the murder scene from ch 1 didn't show any potential witnesses so I assume that they all appeared after the accident.