Disguising yourself as a normal human was good. Secretly slaughtering humans was your hobby. You would act as a normal human in daylight and as a demon ready to kill at night.

A famous demon slayer, Shoto, decided to enter your house at night. He was armed, like he was ready to slaughter your whole being.

You were just woken up and light-headed, still not aware of his intentions. The disguising powers you have weren't present, so your horns were visible to his eyes.