Doggy Style
Finally, finally he was going to get some real alone time with Theodore! Ever since he had been bitten by that werewolf, Alvin and Simon refused to let him out of their sight. Sure, they'd had time together at school (which consisted of more than a few visits to the closet for kisses if Theodore had his way) but they didn't get to spend the night together. Teddy was curious! One of his besties was a monster now and he wanted to get to know that side of him too, especially if they didn't manage to find a cure.
Tonight though, tonight was finally the night. Simon and Alvin had this huge clue they wanted to go investigate, thanks to Alvin's Monster Book of Monster Facts, and they asked Teddy if he would watch over the youngest chipmunk while they went, since they couldn't risk Dave finding out. He said yes, of course, and his Uncle was more than happy to allow the boy over; the kids never caused any trouble.
So Teddy waited, quite impatiently, for his friend to arrive and the second he did, he grabbed his hand and rushed him up to the bedroom. Theodore didn't even wait for the door to be closed before he planted a kiss on the excited corgi, causing him to shiver with anticipation. He knew he had to keep calm though—this night was about watching over Theodore and keeping him safe. They'd have time to play next time around.
They got through the rest of the afternoon, enjoying dinner with Teddy's cousin and Uncle Muta, playing video games on the big TV in the living room, and even watching a 'grown up' movie together (with said Uncle (so long as they didn't tell his other Uncle when he got home, so shhh).
At nine sharp, Uncle Muta sent them to bed and headed off to his own room for the night, leaving them alone at the absolute perfect moment. 
Theodore was transforming. The chipmunk had been about to put on his pajamas when it happened-- a pained whine, followed by a fierce growl as his hands and feet grew more paw-like, thick claws sprouting from the digits. 
His fur thickened, shifting to a darker shade of beige, and the hair atop his head grew longer, covering the sides of his face a chin. Lastly, his ears turned pointed, and his canines grew—there was no doubt that he was a werewolf.
But still, Teddy found him... cute. Theodore was definitely still in the 'puppy stage' of being a werewolf, but something was... off. His face didn't hold the curious innocence his brothers had described. He didn't look like he was ready to run around and play. He looked wary, ready to defend himself—maybe because it was the first time 'meeting' Teddy?
The corgi lowered himself to the floor and called Theodore over, “Come here, boy. It's okay, I'm your friend.” Theodore slowly approached him, walking on all fours, never breaking eye contact with Teddy. “That's it. A little more.” Theodore started sniffing the corgi as soon as he was in range, from his head to his toes, making a little extra attention to his shorts, and what was held underneath.
With a content huff and a nod, Theodore decided that Teddy wasn't a threat... but.. he smelled like something.... something else. The werewolf reached down and sniffed himself, then once again started sniffing Teddy, even knocking him over and sticking his little snout against Teddy's butt.
That was it. This... yellow puppy was his. He belonged to him. There was no other way to explain why his scent would be all over the corgi, in his fur, on his clothes, coming from all over him, a hint even from inside. 
Theodore growled with excitement, ripping off his underwear as he crawled on top of  Teddy, pinning the corgi down as he started to rut against him. His cock began to harden and as it did, the faster and harder he humped. 
“T-Theodore--!” While not exactly pleasurable for himself, having the heavy weight on top of him and those hips slamming against him was definitely turning him on. “Heel, boy!” The werewolf had no intention to listen to anything Teddy said, though. He just kept on going, huffing and growling.
With all his strength, Teddy rolled away from Theodore's grasp, panting, his own little red cock poking out of it's sheath, tenting his shorts. Unfortunately for the corgi, Theodore didn't like having his playmate escaping from him, and proceeded to tear his shorts and underwear to pieces (leaving small scratch marks here and there), before dragging him back by his ankles.
Teddy stared up at Theodore, who pinned him down once more, and reached for the bottle of lotion he kept on his bookshelf, hoping he'd have time to (literally) save his ass. The more he squirmed and fought against the werewolf, the angrier he got, and when his paw finally grasped that bottle, Theodore let out a roar. It wasn't loud, it was squeaky and actually kind of adorable but it got the point across.
With ease, Theodore flipped him back onto his hands and knees, shaking himself off as he got ready to mount the corgi again. Teddy took the few moments to squeeze a glop of lotion onto his paws, using it to coat his ass, fingering himself to ensure he was somewhat prepared for what was to come.
Once again he was down, Theodore's weight holding him in place as the werewolf lined up his cock just right, now that there were no barriers between them. “Rrrnnn..” A noise of pleasure came from Theodore as he slid into Teddy's waiting ass, his cock bigger than the corgi remembered..with a small knot at the base, similar to his own.
He couldn't help himself. He tried, he did, but this was Theodore and he was so... so aggressive. Teddy moaned loudly, pressing back against the cock, wanting all of it and more. It was as though Theodore could sense it, sense his mate's wanting, because he didn't hesitate, growling into Teddy's ear, lapping at his neck and shoulders.
It was so much, so hard, so fast, so much pleasure that it edged on pain, and Teddy's cock was constantly dribbling puppy cum onto the floor below him. “Awroof!” Teddy let out a bark, panting happily as he wagged his tail and shook his ass, tightening around the cock inside of him.
Theodore took it to mean he was doing a good job, and began fucking his bitch with as much strength and speed as he could muster. The only thing going through his head was mine mine mine MINE as he bottomed out, little knot planted inside the corgi as he began to cum. Unlike Teddy's own cum, Theodore's was heavy and thick, building up inside him.
Teddy was shaking with pleasure as he shot out a final stream of cum onto the hard floor, collapsing happily as Theodore's cock slid out, a string of cum visible, leading from the tip to Teddy's ass. The corgi rolled over, onto his back and sat up, watching as Theodore started to clean himself off—but he was still half hard. Which meant they weren't done yet...
A short whistle got Theodore's attention and Teddy growled at him, getting on all fours himself. He could play the big bad dog if he had to, just to get what he wanted. He crawled over to Theodore, who was not watching him with curiosity, and climbed on top of him, taking hold of the pale pink cock, and holding it in position so it would slide back into his ass.
Not finding a problem with this at all, Theodore lied back, allowing Teddy to do as he pleased. And he did.
Raising his hips, he slammed himself down on Theodore's cock, biting down to muffle the scream that almost escaped him. It felt so good and he just wanted to keep going and going-his ass could take it, his cock could take—so what if he got got scratched up. After all of this, his only regret was going to be that Theodore wouldn't remember it all in the morning.
He bounced on that wonderful werewolf cock, squeezing it, popping the knot in and out, sliding from the very tip to the base, not even daring to touch himself because he know he'd be able to come again, just from this.
Their moans filled the room, growls and huffs and yips as well. Teddy no longer cared if anyone heard them, he didn't care about anything at all except the werewolf below him, and his cock. They were getting close, both of them. Teddy could feel it. He was going first—he felt it building fast, and faster he bounced, cum shooting from his little cock all over Theodore's stomach.
He rode out his orgasm, wanting to feel that pleasure wave for as long as possible while bringing Theodore to the edge. The werewolf was panting heavily, writhing and thrusting wildly until finally, he released a second wave of cum into Teddy. A hard shudder ran through him as he dug his claws into the corgi's hips to keep him in place, making sure every last drop made it inside.
They stayed like that for a while, just basking in the afterglow, neither wanting to move. It was quiet, peaceful, and even loving as Theodore reached up and licked all over Teddy's face
Once they were done, Teddy helped lick Theodore clean, swallowing down mouthfuls of both of their cum, and Theodore returned the favour, ensuring every drop was gone from Teddy's fur. With a wide yawn, the werewolf looked over to the bed and jumped up, getting himself comfortable, though watching Teddy, waiting to see what he'd do.
The corgi, not wanting to have cum dripping out of him all over the place, slipped on a pullup from his top drawer, then tapped the light switch and climbed into bed. He'd clean up everything else in the morning. The stars and nearly full moon shone bright in the night sky, illuminating part of the room.
Theodore curled up on top of him, falling asleep within seconds with a soft yawn. Teddy  smiled softly as he looked at him—Now he looked like the happy little puppy he'd been described as. Yawning once himself, Teddy got comfortable and closed his eyes, not noticing the pair of colourful cat eyes peeking in through a crack in the door. The owner quietly shut the door and walked away, having seen everything he needed to see.
Tomorrow was definitely going to be an interesting day.
The End