Big rat snarls and huffs, tugging on his giant cock
Other hand alternates between rubbing his meaty chest, tweaking his thick nipples, or rubbing his melon-sized balls
Snarls as he cums, tail thrashing as jets of thick musky rodent seed cover his body
Lets go of his cock, panting in pleasure
Reaches over for a rag 
Wipes the small amounts of thin seed on his slightly pudgy and hairly belly
Human thinks about how much he enjoyed that fantasy, of being the character, big huge rat
As opposed to his real form, an out of shape human
Dresses up, goes to computer, more info on character's story aside just form (former evil overlord henchman, worked for the mob, mainly works as intimidation/muscle for a mostly legal group now)
Checks email, finds a "Job offer" for the character
Reads it, a bit vague but thinks its a lead for a RP and more character development, sends an email back in-character agreeing. 
Reply comes back almost instantly with confirmation and more vague information, "More info to come"
Doorbell rings, he's not expecting anyone, goes to answer
Nobody there but there's a package with his name on it from "The Delta Organization"
Didn't order anything, takes the package inside, opens up, finds a jockstrap, same style his character wears, in his size
Looks at jockstrap, picks it up, weird feeling rushes over him
Suddenly horny, has an involuntary orgasm 
Belt is slack, takes off pants, finds he's messed all over his underwear, seed even getting his flat belly sticky
Cleans up, then looks at the jock and puts it on instead of another pair
The jock feels great, gently rubs his slightly larger package through it
Watches TV a bit, sees home gym commercial, horniness rises and he faps again, filling his medium clothing out
Goes out to Big Box store for stuff, does mental shopping list
Sees gym equipment, boner rising again and threatening to blow in public
Rushes to restroom, face red, takes care of it
Shirt tears in a few places from growth, like its shrunk in the wash
Smirks at the cute dude who saw him walk in with a boner
Reviews mental shopping list; it's changed
Also picks up some more clothing
Decides to stop at liquor store to pick up some beer
Cock threatens to blow again when he sees a bottle of bourbon like his character drinks
Clerk notices the big sexy man with the throbbing erection straining the pants fabric
"Oh sir, I've got some discounted bottles of that in the back room..."
clerk drags him in, gives a blowjob
Guy cums loads, thicker than before. Shirt sleeves tear, bottom of shirt lifts up exposing thick abs and belly button
Tries button pants before giving it up, "Stupid laundry day, these are way too tight"
picks up two large bottles effortlessly under each arm and walking back out, "Thanks for that, Kid"
Makes it home and unloads his groceries, peels off shirt, exposing thick muscle torso with short bodyhair all over.
Sniffs shirt and makes a face, "Jeez this stinks"
Horniness washes over him again and he falls onto the couch, literally tearing his pants off
Pulls away the jockstrap still perfectly holding his junk despite the growth of his apple-sized balls and cock
Faps again, letting out low snarls
Cums again, several jets of thick seed
USes shirt to wipe himself off, giving it a sniff, "Yeah, that smells nice and masculine"
Gets up, doesn't even try putting on his pants, walks around the house in the jock, only pulling on a pair of gym shorts to answer the door again
Another package from Delta
It's a selection of cheeses
"Why would I want thi-"
Mouth waters at the same time his cock jolts to attention again
Strips himself naked, strokes himself off as he consumes the cheese
Tries to focus on the cock once, but he can't finish 
Feels better while eating the cheese
Finishes the entire thing, feels something building up in him
Snarls and huffs, using one hand to tug at his cock
Other hand alternates between rubbing his meaty chest, tweaking his thick nipples, or rubbing his swelling balls
The hair on his body thickens, becoming a thin fur coat that does not hide the still thickening definition of his body
His hands and feet shift, becoming more ratlike
His tail grows out, long and thick, thrashing with pleasure
His ears, then his head, reshape
"This is just like my fantasy"
"Wait oh god what's happening to me"
Tries to take his hand off his cock, can't quite do it,
Lumbers to his feet, many more pounds of muscle heavier than when he started
Stumbles towards his bedroom, makes it through the first doorway without a problem but his shoulders swell before he makes it in to his room, having to turn sideways and barely fit his thick torso in that way, his ears brushing against the cieling
Everything starts to feel less and less familiar while he falls onto his back onto the bed
Doublestroking now until he cums
Snarls as he cums, tail thrashing as jets of thick musky rodent seed cover his body
Lets go of his cock, panting in pleasure
Reaches over for a rag 
Wipes down the thick seed off his fur coat as best he can with the limited range of movement he has
His cock gives a twinge of pleasure as he feels how little he can reach, his size turning him on again
Tugs on his cock a few more times, enjoying the increasingly familiar sensation of being a huge rat
Email alert on the computer
Goes to look
"Thank you for completing the job, character. Proper clothing will be delivered to you shortly. We would like to offer you a permanent position with Delta, if you're interested, return with the delivery driver."
Tugs on his cock some more, considering, then says "Sure why not"