Dabit deus his quoque finem

Dabit deus his quoque finem is the 4th volume in the Youjo Senki Light Novel series.

Short Summary
The day of the Empire faced another crisis.

Rus Union start to mobilize their troops.

Who will win the Eastern battle? Who will succeed?

Will Tanya finally find her own peace and win against Being X?

Chapter VI: Operation Door knocker
That ends 470+ pages of vol 4.

Thanks to u/MSG_Johnny2 who posted the summaries at r/YoujoSenki.