While most of the portals show fantasy worlds or other countries, the one that most intrigues you is one that seems to show this tent at the other end. Is this the scam one where if you go through it, nothing happens, you wonder? In any case, you want to know more than you want to go into any of the others, so you step through it, your body seeming to walk automatically on the spot like a predetermined animation in a video game.
After a few steps, the tent behind you seems to vanish and your clothes follow suit as you continue to walk through it stark naked. "The Parallel World portal, huh? Interesting choice," you hear Riley say, assuming it's pre-recorded but not really being sure in all honesty. "It's fascinating how tiny changes can so dramatically affect larger things. In this portal's case, what would you be like if a single chromosome of the genetic code of the sperm that created your body was an X instead of a Y? Well, you'd look like this..."
As he finished his monologue, something about you felt... different. You shivered with anticipation as indescribable sensations swept your body. Your facial structure seemed to soften and your larynx shrank, turning your voice higher-pitched. Your arms and legs and hands and feet shrank slightly, as well as losing most of their body hair. Your figure tugged inwards and shrank in places while widening and enlarging in others (particularly your hips), your skin turning suppler and smoother all over. Your chest felt dramatically more sensitive and your nipples perked up, large mounds forming under them as you sprouted C-cup breasts. Your penis irrepressibly shrank back into your body as your testicles were pulled up inside you, their whole reproductive function transforming as they connected to something else inside. Your empty scrotum receded until a pair of moist lips emerged at its centre, also joined to what your former testicles had connected to. As if you couldn't tell what your body had become, you looked down to see the last of your penis recede into a clitoral nub.
At last the portal released you and you looked down at yourself, baffled at now having a body that was female. You stood up slowly, and realized that...