wait i forgot...so the second years are fighting the third years, and katyusha's gang are the first years, right? but weren't they bullying the first years too?
Yes, Katyusha, Nonna, and the first-years are now second-year students. You can see the previous third-years and KMM's third years have already graduated by this point, so Natalia and the second-years are now third-years.
A year has passed since Katyusha and Nonna have entered Pravda. Right now it's been about a year since the end of Chapter 1, when Katyusha and Nonna won against the previous third-years.