Nightmares would be a common issue for any child who was exposed to a negative enviroment—such as the League Of Villains. So he wasn't surprised when you showed up seeking comfort after you had one.

"It wasn't real. Calm down." Kurogiri said lowly, patting your head awkwardly. He had other things to do and worry about, aside from the childish nightmare of some kid he wasn't even encharged to take care of. Then again, for some reason it didn't settle well with him to leave you alone like this.