My Unseen Wife Is Skilled with a Machete

On the first day they met, a mysterious girl pulled out a marriage registration certificate with Xin Ye's name on it.

Xin Ye planned to find a time to get a divorce.

On the third day they knew each other, the girl, who shouldn't have been there at all, transferred into his class.

Xin Ye decided to keep their engagement a secret.

Then, on the nth day they knew each other, the girl picked up a butcher knife.

"Hey, hey! This is nothing like what we agreed on!"

(In the vein of the Japanese manga Tokyo Ravens, Shakugan no Shana, and Sword Art Online.)