Public Boundary Marker

James Potter's malicious words were like a boulder dropped into a still lake, stirring invisible ripples across the grounds on this spring afternoon. The gazes of several nearby students were drawn over, filled with curiosity and the anticipation of a spectacle.

Beneath the shade of a tree, Snape spun around abruptly. His face was pale to the point of transparency, his lips pressed into an impossibly thin, bloodless line. A storm, suppressed to its absolute limit, churned within his dark eyes—a look Lin Yanqing had never seen before, a mixture of bone-deep humiliation and barely contained fury. The hand holding the half-processed magical ingredients emitted faint creaking sounds from its knuckles due to excessive force.

"Potter," Snape's voice scraped out as if from an ice fissure, low and dangerous, "take it back."

"Take it back?" James spread his hands exaggeratedly, basking in the attention from the onlookers. "Why? Did I say something wrong? Weren't you two just here... hmm? On a secret date?" He deliberately drew out his words, eliciting a snort from Sirius and even a grin from Peter.

"I said, take it back!" Snape took a step forward, his wand already in hand, emanating such a chilling killing intent that the very air around them seemed to freeze.

Lin Yanqing had also walked over by this time. He didn't stand beside Snape but stopped at a position that created a pincer formation with him without appearing overly intimate. His expression was calm, his gaze sweeping over James and Sirius before finally settling on Snape's taut profile. Through their contract, he could clearly feel the destructive energy about to erupt accumulating within Snape. Once they acted, Snape would inevitably be in a disadvantageous one-against-many situation, and likely lose his composure in his rage.

He can't make the first move.

Just as James was smugly preparing to add fuel to the fire, and the moment Snape's wand was about to rise towards him—

"Mr. Potter seems to have a rather unique perspective on interpersonal relationships," Lin Yanqing began. His voice wasn't loud but clearly reached everyone's ears, carrying a Ravenclaw-esque coolness akin to academic discourse. "However, conflating academic collaboration with baseless speculation and using it as a weapon to attack others doesn't exactly embody the 'chivalry' Gryffindor professes to uphold."

His words skillfully shifted the focus from the insulting accusation of "relationship" to "academic collaboration," and then counterattacked, accusing them of betraying their house spirit.

James was momentarily stunned by this unexpected response, unable to find a suitable retort.

Sirius, however, let out a cold laugh, his grey eyes fixing sharply on Lin Yanqing. "Collaboration? A Ravenclaw and a Slytherin, meeting in a secluded spot during their free time to 'collaborate'? Collaborate on what? Dark Arts?" His accusation was even more insidious.

"What we collaborate on is hardly something we need to report to you, Black," Lin Yanqing's tone remained steady, but his eyes sharpened. "Just as we wouldn't inquire about the three of you being inseparable, whether you're 'collaborating' on planning your next rule-breaking prank, or something else... more unsavory."

"You—!" James roared in anger, his wand snapping towards Lin Yanqing.

Almost simultaneously as James raised his wand, through their contract, Lin Yanqing clearly received an incredibly swift and precise prediction from Snape—"Leg-Locker Curse! Block lower left!"

Without hesitation, Lin Yanqing flicked his wrist, pointing his wand downwards—

"Petrificus Totalus!" James's spell shot out.

"Protego!" Lin Yanqing's Shield Charm rang out almost simultaneously. An invisible barrier appeared precisely to the lower left of his body, perfectly blocking James's cunningly angled Leg-Locker Curse. The red light struck the barrier, splashing a few sparks before dissipating into nothingness.

And almost the instant Lin Yanqing blocked the attack, Snape moved! He didn't attack James but tapped his wand rapidly. A silent, almost imperceptible magical gleam shot towards the seemingly flat patch of grass beneath James's feet—

"Muddying Charm!" An improved, highly effective version of the soft mud curse!

The solid ground beneath James's feet instantly transformed into a viscous, slippery mire! He was momentarily stunned by his attack being blocked, and his feet suddenly gave way. Losing his balance, he let out a startled cry and fell backward, landing with a plop right into the mud he himself had created (and which Snape had magically enhanced). He was in a pathetic state, his wand flying out of his hand.

All of this happened in the blink of an eye. From James's attack to Lin Yanqing's precise block, to Snape's insidious follow-up, it took no more than two to three seconds. The seamless coordination and the swift, ruthless counterattack stunned everyone present.

Sirius and Peter stood frozen, unable to react for a moment.

Snape remained where he was, wand still in hand, his face as cold as ever. But in his dark eyes, the storm had subsided, replaced by a cold, almost cruel satisfaction. He watched James struggling and cursing in the mud, the corner of his mouth curling into a barely perceptible, mocking arc.

Lin Yanqing slowly lowered his wand, his gaze calmly falling on Sirius and Peter. "Are we going to continue?"

His tone carried no provocation, merely stating a fact. But coupled with James flailing in the mud beside them, and Snape's wand, which looked ready to unleash even more vicious spells at any moment, the question was filled with menace.

Sirius's face turned ashen. He stared intently at Lin Yanqing, then glanced at Snape, who was watching with cold indifference. He knew they wouldn't get the better of them today. This Ravenclaw was more troublesome than they had imagined, and Snape... he seemed to share some peculiar understanding with this Ravenclaw.

"We'll see about this," Sirius gritted out, bending down to pick up James's wand. Together with Peter, they laboriously pulled the incessantly cursing James out of the mud. The three of them, covered in mud, hastily retreated amidst the suppressed snickers of the surrounding students, their faces streaked with dirt.

Quiet returned to the edge of the grounds, but the atmosphere had changed.

The gazes of the students who had been watching the spectacle now held a mixture of surprise, scrutiny, and even a trace of unconcealed apprehension as they looked at Lin Yanqing and Snape. They had just witnessed how the two of them, working together, had so easily put the Marauders in their place.

Snape didn't look at Lin Yanqing. He silently put away his wand and bent down to pick up the fallen materials, carefully brushing off the grass clippings and dust. His movements regained their usual precision, but the icy hostility around him had not entirely dissipated.

Lin Yanqing also remained silent. He could feel from the other end of their contract a cold sense of exhilaration, like a long-awaited revenge, and a feeling of stability... after establishing a certain "boundary."

Snape finished packing his things, straightened up, and finally turned his head, his gaze sweeping quickly over Lin Yanqing. His eyes still held little warmth, but the previous rejection or scrutiny was gone, replaced by something akin to... a cold acknowledgment, like looking at a useful weapon.

Then, without a word, he turned, cradling his materials, and walked steadily towards the castle.

Lin Yanqing watched his retreating figure disappear into the castle's shadow, then looked down at his own hand, which had held his wand.

This time, they hadn't exchanged any items, nor passed any notes.

But together, they had erected a boundary marker—an action that declared to everyone that their "connection" was inviolable. Anyone who dared to cross this line, who defiled it with foul words, would pay the price.

This boundary marker was forged from cold understanding, precise tactics, and ruthless retaliation.

It stood silently in the Hogwarts spring afternoon, marking the formal establishment of a new alliance that no one could ignore.