Naraku betrayed everyone.

Every underling he had ever created, every person he had struck a bargain with, every demon he had tricked into working for him. Everyone.

Kanna was his most perfect creation. She knew exactly what she was, exactly what he was, and exactly the way of the things around them. She was surprised at nothing, for she watched everything.

Unlike the others, she expected treachery, to be used and eventually disposed of.

So he didn't. Instead, he made her his trusted one, his indispensable one. He found a way still to deceive her expectations.

For Naraku betrayed everyone.