Tag should be used if the main protagonist either is being blackmailed or is the one doing the blackmailing.

Blackmailing the act of getting money from people or forcing them to do something by threatening to tell a secret of theirs or to harm them.
I fell in love. Her name was Shirasaki Yukino. I could only look at her from a distance. However one day I heard that she already had a boyfriend. Even if I love her, I can’t have her. The devil sent me an invitation. I can make her mine!
Navier was the perfect empress, however, the Emperor wanted a wife, not a colleague. And so, the Emperor abandoned Empress Navier and placed an ens*aved girl beside him. That was fine until Navier heard the Emperor promise the s*ave the Empress’ position. After many ups and downs, Navier decided she would accept being the Queen of the neighbouring country and remarry.