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It started during History of Magic.
Which, Sirius maintained loudly and often, was the cruelest possible environment for two seventeen year old boys hopelessly in love and catastrophically unable to keep their hands to themselves.
“You know what this class needs?” Sirius whispered dramatically from across the aisle.
Remus didn’t look up from his notes.
“A professor with a pulse?”
James snorted into his parchment.
Binns droned on about goblin taxation treaties entirely unaware.
Sirius kicked lightly at Remus’s chair.
“No,” he said. “It needs entertainment.”
Remus finally glanced sideways.
That was mistake number one.
Because Sirius Black was sprawled lazily over his desk with his tie already loose, dark hair falling into his eyes, wearing the exact expression that usually preceded either detention or kissing.
Sometimes both.
“What kind of entertainment?” Remus asked carefully.
Sirius grinned.
“The kind where I make you blush before class ends.”
James immediately muttered, “Oh no.”
Peter looked between them nervously.
Remus merely raised one eyebrow.
“You think you can?”
Sirius looked delighted by the challenge.
“Oh, sweetheart,” he said softly, “I know I can.”
Remus hummed thoughtfully and returned to writing.
Sirius frowned.
“That’s it?”
“You’ve got to try harder than pet names, darling.”
James made a violent choking sound.
Across the room, Lily glanced up suspiciously.
Sirius straightened in his seat.
Challenge accepted.
For the next ten minutes he attempted everything.
Leaning too close under the guise of borrowing parchment.
Brushing his knee against Remus’s beneath the desk.
Murmuring, “You look obscenely pretty when you’re concentrating,” directly into his ear while pretending to ask about homework.
Any of these tactics worked on other people.
On Remus Lupin, they produced nothing more than the faintest twitch at the corner of his mouth.
Sirius narrowed his eyes.
“You’re cheating somehow.”
Remus turned another page calmly.
“I’m simply better at this than you.”
“Impossible.”
“Mhm.”
Sirius abandoned subtlety entirely.
“Last night,” he whispered, voice dipping low enough to send a faint shiver down Remus’s spine despite himself, “you made the nicest sound when I kissed your neck—”
Remus finally looked at him.
Sirius smirked triumphantly.
Until Remus leaned slightly closer and said, very quietly:
“Is that why you nearly cried when I touched your thigh under the table at breakfast?”
Sirius froze.
James slapped both hands over his face.
“Oh my God,” he groaned.
Remus continued serenely.
“You looked so desperate, Padfoot.” His voice stayed maddeningly even. “I almost felt bad for you.”
Sirius’s ears turned bright red instantly.
Remus knew every weak point with terrifying precision.
Not because he was cruel.
Because he paid attention.
He knew Sirius loved being teased almost as much as he loved pretending he didn’t. Knew exactly how flustered he became when Remus’s voice dropped into that soft, private cadence reserved only for him.
Most unfairly of all, Remus looked completely composed while doing it.
Sirius, meanwhile, was already unraveling.
“You’re evil,” he muttered weakly.
Remus offered him a small smile over the rim of his teacup.
“And yet you adore me.”
That was the problem, really.
Sirius did.
Hopelessly.
—
The game escalated over time.
In the library.
At Gryffindor table.
After Quidditch practice, which nearly resulted in Sirius fainting after Remus casually remarked, Your hands look nice around the broom handle, love.
But classes were the worst.
Mostly because they absolutely should not have been doing this while professors were actively teaching.
“Focus,” James hissed one afternoon as Sirius stared blankly at Remus instead of the complicated Arithmancy chart Professor Vector was explaining.
“I am focused,” Sirius lied.
Remus sat three seats away looking infuriatingly put together in rolled-up sleeves and a loosened tie, quill moving steadily across parchment while Vector lectured.
Then Remus glanced at Sirius.
Just once.
Calm.
Measured.
And mouthed:
Good boy.
Sirius forgot his own name.
James physically grabbed the back of his chair before he could fall sideways.
“Jesus Christ,” James muttered.
Marlene looked deeply entertained.
Remus returned his attention to the class like nothing had happened.
Bastard.
Complete, unfair bastard.
Sirius spent the next twenty minutes in absolute agony while Professor Vector droned on about predictive equations and magical probability, and Remus calmly copied notes as though he hadn’t just psychologically destroyed his boyfriend in the middle of Arithmancy.
The worst part?
Remus never looked smug afterward.
Just quietly pleased.
Like he knew exactly what he’d done.
Which he did.
Obviously.
—
“You do realize,” Sirius said later that night while sprawled dramatically across Remus’s bed, “that this relationship has an unfair power imbalance.”
Remus looked up from his book.
“Oh?”
“Yes. Because you can reduce me to incoherent yearning with approximately four words.”
“That seems exaggerated.”
“It is NOT exaggerated.”
Remus tried very hard not to smile.
Sirius pointed accusingly.
“See? That face right there. You know exactly what you’re doing.”
Remus closed his book carefully and set it aside.
The dormitory was quiet for once. James and Peter were downstairs, commandeering the common room for a chess match.
Moonlight spilled silver across Sirius’s hair.
“You started it,” Remus reminded him softly.
Sirius scoffed.
“I was flirting.”
“You declared war.”
“A fair point.”
Remus shifted closer on the bed.
Sirius immediately lost track of the conversation.
Because this was another unfair thing about Remus Lupin:
He didn’t seem aware of how devastating simple affection became in his hands.
The brush of knuckles against Sirius’s wrist.
The soft look in his eyes when Sirius talked too fast about something he loved.
The quiet little there you are expression whenever Sirius entered a room.
Remus touched him like he was precious.
It ruined Sirius for everyone else.
“You’re staring again,” Remus murmured.
“You make it difficult not to.”
Remus’s mouth softened.
And there it was.
That look.
The one that always cracked Sirius open from the inside out.
Fondness so intense it bordered on reverence.
Sirius swallowed hard.
“Oh, don’t do that,” he complained weakly.
“Do what?”
“Look at me like I hung the moon.”
Remus’s expression turned unbearably tender.
“But you did.”
Sirius made a strangled noise and collapsed face-first into Remus’s shoulder.
Above him, Remus laughed quietly and threaded gentle fingers through his hair.
“See?” Remus said. “Far too easy.”
Muffled against his jumper, Sirius grumbled, “I hate you.”
“No, you don’t.”
“…No,” Sirius admitted miserably. “I really, really don’t.”