Yeah...Chiaki's sudden shift in attitude is so jarring, page 9 she should've shown some unwillingness to hurt her friend but then forced to cooperate when reminded of the swatter. Here she just looks like she enjoys torturing her friend for no reason. Sure you can have her enjoy torturing her friend, but that's supposed to be after a dramatic corruption. Like the MC whispering in her ear: "If Hina didn't bully, ...bla bla blah, none of this would've happened and you wouldn't have to suffer like this." planting the seed, then this change would occur.