This is such a weirdly paced manga... I understand the need to keep a mystery going while addressing the plot at hand, but it's super forceful right now with the info we're getting as a reader and not getting a breath. The pace is seemingly fast and we're going to be told the girls stories mainly through flashbacks at this point... but at "this point" we are less than 3 full chapters in.
It's kinda hard to remember what the fuck was going on in this manga between the chapter releases; it's not very engaging. The teacher seems shitty, dumping responsibility on a random student. I feel the masked girl sort of looks neat though.