My man Kazuya did it, although he doesn't know it, Chizuru heard all of it.
I think Kibe already knows Kazuya made a fool of everyone regarding his relationship with Mizuhara and that's why he made Kazuya pay the beers and told him he won't tell him the reason why he went to pick him 2 hours earlier than usual and made Kazuya pay the beers. He's supressing his rage against his friend because Mami told him.
Also, nice ominous foreshadowing about Nagomi possibly finding out the truth too and going full seinen manga broken psycho (grand)mommy over Chizuya's relationship. Kazuya showed lots of balls here by stating he'll stand by Chizuru's side.
I think next chapter won't be as big as this, and mostly because Kanokari day is near (it's on feb. 17th,the same day chapter 176 is out. They'll save the big habbening for that chapter).