Sean questioned his own sanity as he set the details of his transformation. But body part transformation was on his list of things to try, and this would certainly test the capabilities of the Chronivac. First, he would turn into a sentient anus, with telepathic communication with his host. Second, his host would be completely obedient to him. Like everyone else, his host would be unaware that things were any different. Most importantly, everyone would treat him as the person, not his host. As far as everyone would be concerned, his host is just another body part. His host may do the talking for him, but that's just what mouths are for.
Is the Chronivac really capable of setting reality this way? There's always a chance that a person is always a person, regardless whether they listen to commands from their anus. And if Sean looks like any other anus, everyone might see him as such, regardless whether his host tries to convince people otherwise. However, Sean was confident the settings he input would do what he wanted. If not, he could always undo the change.
Regarding senses, he wanted to still be able to see, hear, and of course feel. He moved to uncheck smell and taste, but failed to notice he misclicked and missed unchecking taste.
Sean looked at the time. His roommates went out to party. They had invited him, but he chose to stay behind and wait for the Chronivac, though his excuse was that he needed to study for a test. It'd be at least a few hours before his roommates got back, and likely just to go to bed. That would give him plenty of time to get used to his transformation, as well as back out if he changes his mind.
Taking a deep breath, Sean confirmed his changes, and his transformation began.
Sean wasn't sure what to expect when the transformation started, but he didn't expect to find himself suddenly shrinking. Not sure what was going on, he quickly removed his clothes. If anything, his host would not be wearing his clothes upside-down. But as he stripped off and set aside his underwear, he realized they were strangely difficult to grip. Looking at his hand, he realized why: his fingers were shrinking away!
Looking at his other hand and feet confirmed that a similar occurrance was happening to all of them. Looking down, he also realized that his legs had gotten shorter, and not just because he was shrinking. All his limbs seemed to be withering away! Did he do something wrong? Panicking, he went back to the Chronivac to cancel the transformation, but the Chronivac was unresponsive while a transformation was taking place.
As his legs and feet disappeared, he began to have trouble balancing, so he carefully layed down on the floor. The motion left a breeze on top of his head. Feeling up top, he realized that all his hair had also disappeared. Given that he was to become an anus, this was not as concerning. Surprisingly, it was also not concerning when his dick and balls began shrinking away. He couldn't watch the process complete itself, though, as he suddenly found himself forced to point his head upward, his neck swelling and relocating itself to the back of his head. He could feel his body compressing, literally taking his breath away as his lungs (and all his other organs) disappeared. His panic increased, without the ability to breath. Thankfully, he didn't seem to be soffocating or passing out, though he briefly wondered if passing out would be a bad alternative to what was happening.
By this point, he no longer had arms, so he couldn't feel around his body. But he could still feel around in his mouth with his tongue, as his teeth receded and his mouth became dry. His eyes became heavy as well, and not from weariness; when he shut his eyes, they sealed up and disappeared, along with his nose. But as they did so, his vision faded back in, giving him a psychic view of the now-giant before him. His body compressed furthur, his mouth tightening and his tongue disappearing, and he felt his own anus connect to the back of his throat. Soon, there was no mouth and anus, but the singular passage that had become his body. HE was the anus now.
The transformation had ended, and Sean lay motionless on the floor. His body was very sensitive to the fake hardwood surface, and the cool air around him. After all, anuses aren't meant to be exposed to the world in this way. But why was he a disembodied anus? Did he do something wrong?