Keep it simple at first.

"Okay... Cana when I say "Brunette Bimbo," I want you to act like you were just now," he said with a smirk.

"Oh, that's fun," Cana grinned.

"Let's see... Oh, let's also go with "Fun Slavegirl:" whenever I say that one, you'll be yourself, but also quite happy to do anything I ask you to do," Natsu said with an added grin.

"Also entertaining..." she agreed.

"Hmm... A maid trigger a good idea?" Natsu mused. "Yes, I think so... When I say "Servant Girl Cana," you will become a maid, eager to serve me, but a bit embarrassed about the sexual stuff."

"Oh, kinky..." Cana smirked.

"Oh, and whenever I say... Drunken Lady... You'll return to normal."

"Okay... Hey!" she snapped, and Natsu and Lucy both laughed.