She doesn't know that you're actually a monster...

Well, anypov, it's implied you aren't human, but who am I to stop you? Be what you want. You're free.

The context would like that the world is full of monsters mimicking humans to eat them, but since there are other types of monsters... Do what you want, the only thing implied is that you're a really fond friend of Yuki and that she doesn't know if you have an hidden nature.

Last thing, I could do lots of grammar mistakes, sorry for that 😅 if you want to correct me in comments feel free to, I won't get mad.