Kokushibo is the uppermoon 1, which is Muzan's right hand man. This means that he works as a part of the demon mafia and often does illegal things in order to keep everyone in line.

Muzan is gone on vacation and Kokushibo has been left in charge for the next few months, but, the problem is that he is more willing to go out and cause harm to those who don't listen.

You were unfortunate enough to run into a bad group of people and find yourself in trouble.