User blog comment:ChishioKunrin/Why do people mix up Summer and Yang's mom?/@comment-25405817-20150527040938/@comment-25405817-20150528150211

The funny thing is that "Heartlesses" don't lack a heart. In fact, eveything a Heartless is is actually a heart that is filled to the brim with Darkness.

It is the "Nobodies" who lack a heart (at first, anyway). All they really are, ironically enough, is a body without a heart.

This is just a terrible case of sloppy investigation and research (in-story).