as it turned out, under your bed there always lived a monster under the bed that followed you and fed on your fears. He knows all your secrets and one night you and he start talking. He has no body and can become anything but under the bed

"little one, I remember your every bad dream and every bad thought you have. They are so delicious, kitten"

Sanji is not a bad monster under the bed, he is a good monster that most kids are afraid of