Well, that answered that question. Zack was able to change anything he wanted, and everyone else would just believe that it was normal. Now that he knew this, Zack figured that it was only fair that he had more fun at his sister's expense after everything she put him through growing up. And that last comment of hers gave him an idea.
"What are you talking about?" Zack said, silently making a wish as he walked into the room and closed the door, "You can't change yourself. That's why I do it for you."
Susan scowled at him, "Ugh, you don't have to remind me." She hopped up onto the large changing table that used to be her dresser and laid on her back, "Just hurry up, I've got a lot to do today."
Zack made his way to the changing table with a smirk. He didn't know the first thing about changing a diaper, but that was easily fixed with another wish. He grabbed baby wipes, baby powder, and a fresh diaper from under the table and set them out before reaching over and undoing Susan's diaper. As he pulled it open, he couldn't help but stare at Susan's now exposed pussy. She used to freak out if Zack so much as caught her in her underwear, so having her vagina so casually exposed to him was something new to him. And a little arousing, if the sudden tightness in his pants was any indication.
"Are you quite done perving on me?" Susan asked, snapping him out of his trance, "Get to it already! Jeez, I'd imagine that after so long doing this you'd be used to seeing it by now."
"And I'd imagine that after so many years of having you diaper changed, you'd have learned how to do this yourself by now," Zack shot back, careful not to make it a wish, "Now lift."
Susan lifted her butt up so that Zack could pull the wet diaper out from under her. "It's just too complicated, ok?" Susan said, her face turning red, "Every time I try to learn, I just get all confused and turned around."
"I don't know about that," Zack said, throwing away the used diaper, "It seems pretty easy to me. Of course, you wouldn't have this issue at all if you just learned to use the potty like other girls your age."
Susan glares at him. "Just shut up and finish," she snaps as a tiny squirt of pee comes out of her pussy.
Zack tried his best not to snicker as he grabbed the baby wipes. This was just too good! He was glad he didn't actually alter Susan's personality towards him, because if anything her constant bitchiness about the whole thing was making teasing her like this even more fun. He wiped the pee off of the inside of her legs before doing her crotch. Susan flinched as the fresh wipe came in contact with her pussy, "Cold..." she muttered under her breath.
Feeling mischievous, Zack teased her pussy a little as he wiped, and was rewarded with a stifled moan. "Careful down there!" she gasped.
"Enjoying this, aren't you?" he teased as he wiped up the additional wetness his actions created.
Susan glared at him again. He just chuckled and said, "Lift."
Susan lifted her butt once more, allowing him to wipe her backside. Zack then slid the new diaper under her and added a sprinkle of baby powder. He smirked again as he gave her butt a quick slap.
"Ouch!" she yelled as she dropped down onto the diaper, "What did you do that for?"
"All part of the process, remember?" he said, careful not to snicker too loudly as he made another wish.
"Yeah, but did you have to do it so hard?" she asked with a pout.
"Maybe it'll remind you to be more grateful next time," he replied as he closed up the new diaper and taped it shut, "Alright, all done. Hopefully you can go for more than a few hours today without another change. I have a birthday to celebrate, after all."
Susan sat back up, looking irritated, "Alright, there, you changed my diaper. Happy?" She pointed at the door, "Now if there's nothing else you need to do, get out! I need to get dressed."
She still considered herself the boss of him, huh? Zack wondered if she deserved to be messed with some more...