gripping a pair of briefs in your hand that you were contemplating on your next move while rubbing your palm along the material. You gotta investigate it, but that would mean trying it on. discarding your shoes as you were stripping off your pants and underwear that you even took off your shirt and through them to the corner of the room.
surprisingly, you felt the cold air against your junk and shudder that you hurried it up and slipped a pair of briefs (underwear) on. Much to your surprise, the brief felt really nice and snug against your cock as it was a good fit while feeling the oily surface coat the surface of your organ. it was almost like you had fur, to the point.
"wow, this feels great! why do they call them beast briefs?" you said to yourself with excitement while feeling your penis stiffen as it rubs against your new briefs. You soon feel the warm precum leaking in your briefs, dribble in them as you reach your hand over and furiously started to jack off. you can't stop yourself as you continue stroking and stroking your erect cock, awaiting your climax.
You continue to masturbate furiously and loudly as you near the peak as you felt embarrassed though that you soon let out a loud moan of excitement and pleasure as you fill your brief with your cum. feeling satisfied as you didn't even try to stop it while grinning that you didn't notice something else was happening till later. something was spreading all over your body as you begin to transform into a monstrous new form, to accent your new you as you were turning into....
(this is where you get to decide what the beast briefs/underwear turn you into. feel free to add you own ideas below as a few are listed. thank you and have fun reading"