What a lame chapter. I'm not saying that any of those things introduced in this chapter are lame in themselves, just the way they're presented. "Oh and by the way this totally evil-looking teacher that turned out to be cooler than he looks has this tragic thing that happened to him" a few pages later we learn about this sister we never ever heard about and she's already antagonistic to one of the protagonists. As I said, I'm fine with all of this, just the way it's presented is... Oof...
I feel like the teacher is fine cuz it fits the whole unseen theme of the manga, but the sister, I'm not sure what to make of her just yet. I mean, her caution isn't unwarranted, tho exaggerated