User blog comment:J.hustlah08/Superior Devill fruits/@comment-38.112.107.82-20150416130503

Hobi hobi no mi actually makes a lot of sense when you think about it. It has to do with toys. When you play with toys, you can make them do whatever you want; hence the contract.

Also, since you're a kid when you play with toys (youth power), you're probably kind of selfish, so you don't want your toys to be taken away, so cutting all ties that your toy had to others is a necessary measure to keep them as your toy.

Kage kage no mi was basically the same thing, but with shadows. Shadows, like toys, will follow whatever you make them do. But since you're not turning the person into your follower, just the shadow, the fruit has a whole different set of side effects.

As far as I'm concerned, they fall into a sub-class of paramecia together.