The first few days with Deku were…

Tense.

That was the best word Katsuki could think of to explain it.

The first day, Deku slept, which wasn't a surprise.

Extreme lethargy had been discussed/disclosed in the 'terms and use' section which he had read thoroughly.

He made good use of that time, so the wait wasn't completely intolerable.

Katsuki explored the new and exciting landscape of Deku's body, from his puppy-soft toe pads to his glorious new hole hiding beneath his bushy tail.

Did he take his time seeing how wide he could stretch it before his pup started whimpering in his sleep?

Fuck yeah he did.

Did he jerk off into the soft fur of his rump intending to have Deku clean himself up once he woke?

100%

It took every fiber of his being to not grab Deku by the back of his neck and fuck him into the carpet right then and there, but a part of him, no matter how small, wanted Deku awake during his first time.

He wanted Deku aware as Katsuki molded his insides to his exact shape.

He wanted to fill Deku up so full that his abdomen bulged with the pressure.

He wanted to watch the cum drip from his spent hole, pink and gaping and utterly ruined.

He wanted Deku to limp and whimper afterward.

These were all things worth waiting for.

The second day was a challenge. Deku had woken up terrified. Then had the audacity to act indignant, as if his body was not Katsuki's to do with as he pleased.

It didn't sit well with Katsuki but now was not the time for harsh words or punishments. That would come later, once Deku had relearned who he belonged to.

So for now, Katsuki feigned gentleness and concern and understanding, all with a twitching eye and a boner which Deku definitely noticed.

And pointedly ignored.

Katsuki almost snapped, because how dare he?

Did Deku understand how much Katsuki had paid to make him perfect?

Katsuki hooked the leash to Deku's collar and dragged him to the door. If Deku wouldn't acknowledge what Katsuki'd done, if Deku didn't realize how much he should be THANKING Katsuki right now, he would use the newfound adoration from strangers to his advantage.

At first, Deku was a little shit, forcing Katsuki to muscle him outside the high end apartment building and onto the sidewalk.

Deku froze, shaking his fluffy head, whimpering and cowering then pissed all over the sidewalk.

What Katsuki would have given to see Deku blush at what he'd done, but before he could do anything an older man in a business suit and slicked-back red hair walked up to him.

"Woah Baku-bro! I didn't know you had a dog! He's Gorgeous! What is he?!"

Katsuki answered, smirked, then watched the man fawn over Deku.

The poor thing looked stunned and warry, as if any second this man would discover he was a quirkless loser and retaliate.

But he didn't. He dropped to his knees in his expensive looking suit, and cooed, "Who's a good boy?" He bathed Deku in affection, petting and ruffling his fur, getting green-black fur all over his clothes.

Katsuki's smile grew when, within minutes, Deku's tail was wagging and his eyes were bright.

Something primal coiled in Katsuki's gut as they continued their walk.

"Can I pet your doggie?!"

"Awe, he's so cute! Does he want a treat?"

"What a rare color for the breed, stud him out!"

"He's so smart! It's like he understands me!"

They cooed at him.

They spoiled him.

They touched him.

The way strangers looked at him, so soft and endearing, like suddenly everyone who saw him found value in him.

This floofy ball of sunshine demanded more respect and adoration than his human form ever had.

Katsuki knew Deku was coming to the same realization and watched as his desire to be human began to dissolve.

He settled. He obeyed. He looked at Katsuki like he'd personally hung the stars purely for Deku's enjoyment.

His tongue lolled out of his mouth. He pranced beside Katsuki and Katsuki knew everything was going to be fine.

That night, Deku didn't sleep in the kennel had bought to set boundaries. (something about Deku being a pet, not a partner)

Katsuki would never admit as much, but when Deku looked at him with those big, sad eyes at the mention of a cage, he couldn't stand it.

After all, Madame had emphasized the importance of making an emotional bond. Kindof-(not really)-platonic bed sharing was a good way to do that? Right?

Katsuki allowed Deku and his cloud of fluff to sleep with him and it was the best night's sleep he'd ever had.

The third day was…awkward.

The third day, Deku explored his new body for himself, discovered there were new places his muzzle could reach and also discovered the horrors that were "potty breaks".

Having to do his business in public while sick basterds, including Katsuki, watched was almost too much for him. But the very obvious tent in Kacchan's sweats had him second-guessing his embarrassment.

The idea that Katsuki had found him attractive as a human was absurd in and of itself, but now? With this animal body?

It didn't make sense.

The sexual tension was there, Deku could feel it in the new lingering touches. He could smell it in Katsuki's persistent scent of arousal.

Katsuki could tell the nerd was hesitant to partake of such things in his new body. But Deku was lost without his routine.

Katsuki had conditioned him well in the last few years. At the sound of Katsuki's zipper he began to drool like some x-rated version of Pavlov and his bell. Deku craved the taste of Katsuki's cum, longed for the weight of his cock in his mouth.

He was alive to take care of Katsuki, in every way and though he seemed to have forgotten about that these last few days, the compulsion was building.

But the idiot fought it and Katsuki smirked at the challenge.

It became his single-minded goal to drive Deku so crazy with want that he stopped caring.

The look of: "Kacchan, that's wrong," he gave to Katsuki when he began lazily tracing his thumb around his hole was precious.

But there was also hunger of the distinctly sexual variety lingering in those emerald green eyes.

Deku had made to scoot away, to deny Katsuki what he deserved, however Katsuki grabbed the base of his tail and slid him back into place.

Katsuki had never shown Deku this kind of affection. It had always been Deku servicing him with his mouth, no matter how he had begged the blond to fuck him.

Eventually he'd stopped asking but now, Katsuki's hand was exploring a part of him he had given up on.

Deku whimpered as his cock slowly emerged from its sheath, red, pulsing, and desperate. The moment it hit the air with intent was shocking. The haze of this new arousal was doing its damnedest to short-circuit his brain, screaming with the urge to "fuck".

Then the slide of a zipper pulled his brain from the downward spiral and he licked his lips, feeling the saliva form.

Katsuki chuckled, the sound dark and it lit every nerve in Deku's body as the blond grabbed his muzzle holding it closed.

"Not this time Deku. I've got a better idea."