Part 5 of Honzuki no Gekokujou.

Ehrenfest’s first winter without Ferdinand is colder and more oppressive than usual. A surprise betrayal within the former Veronica faction makes the purge even more urgent, and the few who know about Georgine’s destructive goals compare her to the Goddess of Chaos. Meanwhile, Rozemyne throws herself into her third year at the Royal Academy, trying to stave off the loneliness eating away at her. She pushes to win over the students of the former Veronica faction, hoping to save their lives, and meets a new archnoble librarian sent from the Sovereignty. Rozemyne also attends her first class of the archduke candidate course—though her personal ambitions mean she is taking the scholar course as well. In the midst of this balancing act, she finds that her environment has changed drastically once again!

(Source: J-Novel Club)

Note: Final part, this entry covers 217 chapters of the webnovel (chapter 461 - 677).