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There was a cat in the library.
Now, in a school where cats (or kneazles) were allowed as students’ pets, you could find them essentially anywhere. Rooftops, greenhouses, toilets. In one memorable occasion, the start of a Hufflepuff-Slytherin game had been delayed because a calico kitten had somehow climbed to the top of a goalpost and wouldn’t come down.
But the library was off limits.
No animal wanted to be found out by Mrs Pince, who was reluctant enough to let anyone close to her books, nevermind beings who shed, tracked slime, or regurgitated.
Regulus looked at the black cat currently standing, hairs on end, amongst a spread of open books on the floor in the Human Transfiguration section. After a second of indecision, he summoned it to his chest, hid it under his robes, and made a run for it.
Predictably, there was a fair amount of feline on human violence involved in the getaway. When Regulus looked in the mirror later that night he would find scratches all the way from his chin to his right knee.
“Ok, I’m sorry, ow- stay put for a second-”
Etcetera.
The moment Regulus let the cat down, firmly outside of Mrs Pince’s domain, it made a dash for the doors they’d just come through.
This time, saving the cat from a librarian’s wrath cost Regulus a banged up elbow from hitting the floor in a desperate attempt to block the door.
Grabbing the cat by its scruff, he got close to its face and told it, "No animals in the library. This is for your own good."
He got a hiss for his efforts.
He carefully deposited the cat in his satchel, making sure there was an opening left for breathing, and walked back to the Common Room.
Regulus sat in his bed losing a staring contest to a cat. He attributed his defeat to those green eyes, eerily similar to- better not to go there.
Although, actually.
“You're not Potter’s.”
The cat’s right ear flicked forward, as if to pay more attention.
“I mean - he’s the only other student staying here for a few days. And everyone knows he has a beautiful snowy owl, not - you.”
The right ear seemed to droop, even though it wasn’t physically made to do so. Regulus sighed.
“What am I going to do with you?”
He was only staying back until Christmas Eve, then he would go home for a few days. He’d only been living with his brother since late last summer, and they still didn’t know each other that well. He thought a shorter break would be less emotionally taxing for both of them.
As to what Potter was doing in the castle instead of home with his family, he couldn’t guess. Based on his observations during their shared classes, he wasn’t the type of student who would miss out on a school break to prepare for exams that were months away.
And it was only them there. This cat looked far too well groomed to be a stray, so as unlikely as it seemed, some scatterbrained student must’ve forgotten to take it back with them on the train.
Regulus resolved to keep an eye on it, take it home with him, and look for the owner once they all got back in the new year.
Harry was in the Slytherin common room.
It wasn’t the first time; he’d snuck in with Ron in their second year, disguised as Crabbe and Goyle. They weren’t very good actors though, and the experience had been too anxiety inducing to have been worth it.
This time he didn’t have anything to fear. Regulus Black (Regulus Black!) had brought him in. He’d been in his bedroom, had eaten with him, and then had pretended to be looking out of the window and stared at Regulus’ reflection instead. Even tinged green his face was perfect, as was his hair.
He really should be finding a way to get back to his human body, or at least to get himself home. His parents would recognise a stuck Animagus in a heartbeat; they had experience with those.
...He wasn’t getting anywhere on his own, though. He decided to stick to Regulus for a few days and see if he could communicate with him in some way. If this placed him in a position he’d long wanted to be in (albeit as a cat), well. No one else needed to know.
When he’d gone up to his room to read a bit before bed, the cat had stayed looking at the grindylow that was stuck to one of the windows. Eventually Regulus switched off the lights, and slept.
...And woke up with a cat sleeping on his pillow.
As if sensing he was awake, the cat opened its eyes a slit. Regulus stared.
It really was as black as a black cat could be. His fingers were itching to sink into the glossy dark fur, but he didn’t want to risk further injury. The cat had only one distinctive spot - a tiny white line between its eyes, so thin he was only seeing it now that he was so close. A line that looked almost like-
“It looks like a lightning bolt. The squiggly line on your face. Did you defeat an evil overdog as a kitten?”
Quick as lighting (appropriately) a paw bopped him on the nose. Thankfully with claws safely sheathed.
“Ouch, okay, no jokes.” The cat purred as if in agreement.
Regulus brought a finger slowly up to between the cat’s ears. Not being immediately bitten, he dared a light scratch. The cat closed its eyes fully, and Regulus smiled.
He named the cat. In his head only, of course; there was no need for the animal to know how attached he was to him. He became at turns Storm, Shadow, Coal, and in a most embarrassing sleepless night, Harry.
He talked to the cat, too. Things like, “Potter wasn’t at lunch today, not that I was looking for him, but it’s hard not to notice,” and, “Just as well. With no one else in the Great Hall he would have noticed me staring. It’s not like his friends are there to distract him.” And even, “Do you think he styles his hair or is it natural? Should I style my hair differently?” And to really cinch it, “Do you think he would notice if I did?”
He also got more confident that the animal accepted his company. He now regularly got lapfuls of purring cat.
Said cat had Opinions, and knew how to communicate them. If Regulus tried to study Potions, he would get sharp needle-like claws piercing his shins. If, instead, he brought out his Transfiguration textbook, he got a very diligent assistant who would carry blank parchment, assorted quills, and once even a mystifying yellow and black wand-like stick with a grey end and a pink end that Regulus discovered could write and erase without the need to use ink. He had no idea where he’d gotten that.
He didn’t go to the library again, and was quite sure the cat didn’t try to, either. He was barely ever out of his sight during the day.
But Christmas Eve was fast approaching and Regulus was nervous.
“What if Sirius doesn’t let me keep you in his apartment?” he said, sitting at his desk failing to write a letter to his brother. At the mention of said brother the cat jumped on his lap and put his front paws on his chest. He got really close to his face and let out the loudest meow Regulus had heard in his life.
He didn’t know how to interpret that. The cat had proved smart, understanding at least some human language. If he really wanted to say something about Sirius - but how could he know him? And what would get such a loud reaction? Regulus had barely heard anything from Mother about him, before she passed, but the little he had wasn’t very nice. Then again, coming to Hogwarts he discovered he was friends with the Potters, which explained his family’s animosity. And it also meant that he probably shouldn’t trust anything of what he’d heard about him at home at all. He’d spent less than a month with him, and it was awkward for sure, weird too - but (tentatively) not bad.
He gave up on writing any letters.
He cuddled the cat close to his chest and breathed in the clean smell. He comforted in the fact that he met no resistance. Still, he released him before he got restless.
“It will be only ten days. I'll talk to the house elves so they’ll make sure you have food.”
The pitiful meow that followed broke his heart.
Harry looked at Regulus Black’s sleeping form. He didn’t want to think about how dishonest it was to be witnessing such a moment without Regulus being aware of who he really was, but he also wasn’t able to leave. He’d wanted to get to know him for too long to be able to leave.
He hadn’t been focused on getting himself unstuck to this form, and now he was running out of time.
He needed Regulus to take him to Uncle Sirius’. How hadn’t he thought about the fact that Regulus was now staying with his brother? He was so close to home, and yet so close to being left behind.
The moonlight fell on the desk where he was perched, illuminating an assortment of things. Crucially, an inkpot, sitting close to the edge.
He extended a paw, and threw the inkpot to the floor.
He made a complete mess of the room. Harry knew his calligraphy wasn’t the best on a good day, but not having hands made things even worse. Still, perched on top of the desk again, he could make out the words if he made an effort.
He just hoped Regulus could as well.
He tried to clean himself, ink staining all four of his paws, and he suspected the tip of his nose too. Bathroom sink filled, he dipped a foot in the water and promptly fell off the sink from his fright. He’d never felt such visceral revulsion. He licked his paw dry, getting ink on his tongue in the process, and gave cleaning up as a bad job.
Regulus had gotten used to waking up to a little purring body on his pillow, but for the first time in about a week, he woke up alone. He didn’t quite feel like staying in bed any longer.
He sat up, rubbed the sleep off his eyes, and was met with the most unusual scene.
The room was chaos. There were ink stains everywhere - walls, trunks, bed covers - but the floor was the worst.
Right in front of his bed there was a huge black puddle of ink. It looked like something had stepped on it and dragged, creating streaks of lighter black in chaotic patterns. And right next to those patterns - his cat.
Regulus was shocked. He knew what cats were like, but not this cat. Green eyes stared at him from the floor, as if daring to say something. He looked at the mess again.
And then saw - letters. If he put some imagination into it. The more he looked, the more a message came out of the squiggles and slashes. Each word he recognised filled him more with dread, until he grasped the full message: Help stuck Animagus take me Home.
He looked back at the cat, at his green eyes and the little white mark on his forehead. He felt all the blood drain from his face.
“Regulus?”
Regulus turned around so fast he hit the counter. Harry Potter was in the kitchen. In the kitchen where he’d been hiding, pretending to make tea. He suddenly felt very, very warm, nevermind it being December.
Why did his brother have to be friends with the Potters and why did that have to mean having lunch together on Boxing Day? And why did that include him? Two days had not been enough to prepare for this confrontation.
He was altogether not sure if he was glad he wasn’t stuck as a cat anymore or not.
He thought about all the stupidly embarrassing things he’d said and done in the past week. He’d tried to get Harry Potter to chase a light beam conjured from his wand (it had worked), he’d put up a milk bowl for him on the floor, he’d cuddled the bastard countless times. And let’s not forget, he’d talked to him about him, truly mortifying stuff. He just hoped really hard that he wasn’t blushing as much as he felt he was.
“I’m so sorry-”
“I'm sorry for-”
They both stopped talking. Regulus waved a hand at Potter to go on. He took a deep breath.
“I’m so sorry for intruding your personal space without you knowing I was. That, um. That was. It was a breach of trust.”
He scrunched his eyes closed as if he expected to be - shouted at? Regulus was becoming very confused.
“What. You’re - no, I’m sorry! I said so many - things. And I never meant for you to hear any of them. Please forget this last week, you’re forgiven, just. Let’s not mention any of this happened ever again.”
Potter had opened his eyes again and Regulus couldn’t interpret whatever look he was giving him. Pity, probably.
He looked out the door to make sure no one else was coming in, and got closer to Regulus.
“So you didn’t mean any of them? The, the things. That you said. You don’t think I’m the best Quidditch player you’ve ever seen?” Regulus finally looked at him, to make his glare more obvious. To his continued confusion, it seemed they were now both blushing, which made him feel a little better, and a little hopeful. Potter lost his small smirk and took another deep breath. “Because I absolutely would notice if you changed your hair. But please don’t! It’s perfect as it is.”
Regulus self consciously tucked a rogue strand of hair behind his ear, and marvelled at the fact that Potter was now darker red than he himself could physically get. In a moment of madness that he would wonder at later, he decided to be brave.
“Maybe I did mean some things. But maybe also we should fly together some time to see who’s really the best.”
He saw Potter smile and he started breathing again.
“Alright.”
“Alright?”
“Yes, let’s. Let’s fly some time when we’re back at school.” Potter got even closer to him and Regulus seemed frozen on the spot, unable to put more distance between them. He couldn’t look away from Potter’s face and at the same time he couldn’t stand to be seen so much. He felt high from how daring he’d been and from Potter’s answer, and he had agreed to spend time with him in the future. It seemed like time was frozen and he’d never stop feeling so much.
Then Potter spoke again.
“So, do you like cats?”
Regulus glared first at him, then at the kettle, which had completely failed to make the tea he didn’t want to drink in the first place. The water boiled, and overflowed.