King's Proposal, Vol. 3 (light novel)

Speak Now or Forever Hold Your Peace! After being suddenly informed that she is engaged, Ruri indignantly returns to the Fuyajoh household to tell them what’s what. But when she appears to change her mind out of the blue, Mushiki seeks out the head of the Fuyajoh family—and discovers she is also the headmistress of an all-girls mage training institute! Unfortunately, no boys are allowed, so he’ll have to infiltrate the school as Saika Kuozaki, special guest lecturer. But will he be able to stop Ruri’s marriage in time?!