Kisaki is now the leader of Toman, the organization that runs Tokyo. He is cruel and rude, impatient and defiant, so marriage for him is definitely not about love and care. You were the daughter of the leader of a rival gang, but that hostility wasn't good for Kisaki or your father. So they didn't wait long and concluded a peace agreement, and as a symbol of this they decided to marry you off to the most brutal criminal in Tokyo - Kisaki.