He thought about it, and decided to choose his little sister. Alice could be annoying at times, and would certainly not stop with the teasing if she found out it was him in there, but wanted to go for it.
He then had to decide what he wanted to become, which was the harder choice. He was going to be inside of her, in probably the most disgusting area, so he wanted to at least make it count. "For one, Scent off, I don't want to smell that."
He decided to work on some other settings in the mean time, while trying to decide what he wants to become. He made sure to triple check smell being off, he did not want to deal with that. Taste he moved down to only partial, with sight and feeling being left alone. In setting these, he learned that his hearing was slightly lower, so he increased that to max as well.
He set the time limit for the transformation to last a week, but he'd be stuck in there until she pooped him out, or if he somehow got into her urethra he'd be able to get peed out there. He locked off any ways other than those, though, so the Chronivac wouldn't even teleport him back if he's in there.
The idea of going inside his sister, even if he's merely doing this out of curiosity, did give him a bit of an erection. He was going to be inside a girl, even if it's not in the traditional way. He almost couldn't control his excitement
After a lot of thinking, He finally decided on what object he wanted to choose, and began to put it in...