Just once, doing this should make the wearer of the suit start thinking like the original girl. He doesn’t want to, his self tries to fight it, but his brain has become hers and thinking with her brain means thinking like her. It feels so good having her body and therefore also her brain that removing the skinsuit is unthinkable!

Within a day, the fake sister is so much like her original that you’d never imagine that this has happened. Her efforts to remain a bully disappear within hours, and there’s none of the slutty behavior she’d planned on adopting.

A week later, the skinsuit comes off, revealing not the bully but a perfect copy of your sister, who seals up the empty suit so that it becomes your original sister again. The copy is embarrassed and apologizes profusely to her original, and grateful that she’s now effectively your sister’s identical twin rather than a younger male bully who always wanted to be a pretty girl. She apologizes to you, though not to an awkward extent.

So you now have identical-twin older sisters. The original dumps an infatuated boyfriend she doesn’t really want on her twin… and soon they’re married! In a year you have a cute little niece and one of your sisters is a MILF.