He's kind to her.

Mr. McKenzie rubbed his face, set her panties down on the corner of his desk and said,

"I know about your history, and I know how cruel some of the girls at this school can be--how freely they **** their powers to hurt others. So, please, be honest with me. Are you being bullied again? Did one of the girls make you take off your underwear in my class?"

Sana didn't know what to do. In the past, adults had been pretty worthless when it came to helping her with her bullies. They'd get a slap on the wrist, at worst, and then they'd take it out on Sana, making her life a living hell. And what would someone with Beatrice's power be able to do if she were mad?

On the other hand, Mr. McKenzie seemed nice, like he actually wanted to help.