The Red Diamonds mafia is known for precision, loyalty, and silence.

Led by the calm yet calculating Choi San, with his steady husband Choi Wooyoung at his side, the organization functions like a family — mature, disciplined, and deadly when necessary. Bambam, Jihyun, Ryujin, Soohyun, and Sunoo complete the inner circle, each trained to read danger before it strikes.

But this time, the danger comes dressed in silk sheets and soft words.

Their new target isn’t a weapons dealer or a corrupt politician.

It’s a sex education instructor named Kim Seungmin.

Officially, Seungmin runs private intimacy workshops for elite clients. Unofficially, he has been seen exchanging information with their rival gang. Whether he’s willingly involved or being used is unclear.

Hyunjin is the only single member of the Red Diamonds — and the only one who can convincingly approach Seungmin without suspicion.

So he’s sent in under the guise of a private lesson.

But when Hyunjin steps into Seungmin’s world, what begins as a calculated mission starts turning into something far more dangerous.

Because Seungmin is observant. Sharp. And far more aware than Hyunjin expected.

— The Red Diamonds rarely handled problems personally.

But Kim Seungmin wasn’t a normal problem.

“He’s been meeting Black Serpent members twice a week,” Ryujin said calmly.

San stood at the head of the table, composed as always. Wooyoung rested a hand lightly against his husband’s arm.

“And?” Hyunjin asked, voice low.

“We don’t know if he’s selling information,” Wooyoung replied. “Or gathering it.”

San’s gaze locked onto Hyunjin. “You’ll find out.”

Hyunjin didn’t hesitate. “Understood.”

Sunoo smirked slightly. “Try not to enjoy the lesson too much.”

Hyunjin didn’t react.

But something in his eyes flickered.

⸻

Seungmin’s studio was warm. Soft lighting. Velvet curtains.

He stood in the center of the room when Hyunjin walked in

“You’re right on time,” Seungmin said smoothly.

His eyes lingered just a little too long.

Hyunjin removed his jacket slowly, folding it over a chair. “I prefer efficiency.”

A small smile tugged at Seungmin’s lips. “We’ll see.”

The lesson started professionally. Communication. Physical awareness. Confidence.

Seungmin stepped closer, demonstrating how proximity alone could shift control.

“Eye contact,” Seungmin murmured, standing just inches away. “It’s about intention.”

Hyunjin didn’t look away.

His hand settled lightly at Seungmin’s waist when instructed.

Firm.

Controlled.

Seungmin’s breath hitched — barely noticeable.

“Relax,” Seungmin said softly, though his pulse betrayed him.

Hyunjin leaned in slightly, voice brushing against Seungmin’s ear.

“I am relaxed.”

The air changed.

The demonstration shifted into something more real.

Seungmin’s fingers traced down Hyunjin’s chest slowly, guiding, testing reaction. Hyunjin didn’t flinch. Instead, he responded — one hand sliding up Seungmin’s back, pressing him closer.

Their bodies met.

Intentional.

Measured.

But no longer just instructional.

Seungmin swallowed.

“You’ve done this before.”

Hyunjin’s lips ghosted near his jaw, not quite touching. “You’re the teacher.”

Seungmin exhaled shakily — not from fear.

From realization.

Hyunjin moved with precision. Every touch deliberate. Every shift of his hips controlled. When Seungmin’s back met the wall softly, it wasn’t rough — it was confident.

And overwhelming.

For the first time, Seungmin lost composure.

“You’re not here to learn,” he whispered.

Hyunjin’s hand tightened slightly at his waist.

“What makes you think that?”

Seungmin’s eyes darkened.

“Because no one this skilled books a beginner session.”

Silence.

Their foreheads nearly touched.

Seungmin’s fingers curled into Hyunjin’s shirt as if steadying himself.

“Red Diamonds,” Seungmin breathed.

Not a guess.

A confirmation.

Hyunjin didn’t deny it.

Instead, he stepped back. A faint vibration buzzed in Hyunjin’s pocket — Bambam’s signal.

Time.

Hyunjin stepped back slowly, straightening his shirt like nothing had happened.

“You’ll be hearing from us.”