"The scroll!" Hinata thought after a couple of minutes wondering what happened and trying to figure out where did Naruto go. She had a rough idea of what the scroll would do, but it would be better to check it more thoroughly so she went to retrieve it, giving Naruto more of that sensation of swaying up and down with each step she took.
The merged ninja wasn't enjoying the ride, but as he was now just a body part of Hinata he could do absolutely nothing but to accept the way he was moving against his will, the way his new body was restrained in a hot and oppresive environment of Hinata's clothes, how sweaty and disgusting it all felt. There was nothing he could do with his usual bravado and energy because thanks to the jutsu, he could feel his chakra was there on Hinata's body, but he could also feel that it was no longer his. Naruto was by all accounts, trapped and powerless. And he felt even more trapped when suddenly Hinata put her entire weight on him, with the two towers that were making him move suddenly being placed in an horizontal position and the entire structure above him pressing with force and sligthly switching as if wanting to punish his entire new body.
Hinata got the scroll, took a seat in a large rock and wiggled a bit until finding it comfortable enough to start reading. From the spying she knew the jutsu was something related with body parts, so at first she thought this was something about changing the traits of the person targeted in some way but she gasped when she understood what the jutsu was actually about. Both because she didn't expect what it was capable of doing and because apparently she was "strong enough" to make it backfire.
"Twenty hours.. that's not good" Hinata grimaced "But does that mean... Byakugan!" Hinata got an idea of where Naruto could be and activated her power to try and locate him, gasping again at what she saw.
"N-Naruto!" she quickly stood up and remained as straight as she could, witnessing an alien amount of new chakra around her butt, and it was A LOT of chakra, but it was hers. She stood up understanding where Naruto was located and was now trembling slightly from the embarrassment and fear, but what puzzled her the most was not seeing two sources of chakra, she knew about the beast sealed inside Naruto but it was nowhere to be seen.
As for Hinata's ass, he was suffering a new level of oppresive environment when she sat down now that he was squished, and felt all the tiny movements she made once she settled into the rock, a tiny change of position meant another part of his body was now receiving the hardest impact. Once he felt Hinata activating her Byakugan and the way she suddenly reacted he tried again as hard as he could to communicate in some way, but it was in vain. All he could do was mentally shout her name because he had no control at all over his new body, and no way to reach her.
Not even when Hinata placed her hand on her butt and, knowing nobody was around, caressed slightly and even pinched her ass a couple of times. Naruto could feel all that, he just couldn't react to it. He felt like a ghost, and after giving up he only prayed Hinata would get some help while wondering how long this failed prank would last. Thanks to the manipulated memories of his clone, he did think this was about changing body traits of a person temporarily, and wasn't even aiming at Hinata's butt, he was aiming at changing her haircut. He didn't know how badly it could backfire and didn't know about the time limit either.
Remaining as still as she could Hinata considered her options. This jutsu was too weird, who could help her with this? Plus it would be a bit embarrassing to explain for her, and probably harm the future Hokage's reputation even. The scroll mentioned a couple of other things, maybe she should try to undo it by herself? In any case, the only things she were certain about were that she.. or they didn't have much time, and that she should avoid sitting down.
What happens next?