Three years later, Nanshi No. 1 High School.

It was the centennial anniversary of the school. Colorful flags fluttered in the breeze, and the once-dilapidated teaching buildings had been repainted. Only the ancient banyan tree stood silently at the edge of the playground, witnessing the growth of one generation after another.

As the school’s most distinguished alumni, Lu Shaodong and I were invited back for the ribbon-cutting ceremony.

The Lu Shaodong of today was no longer the boy on a beat-up bike with grease under his fingernails. He was the founder of LD Racing Tech, dressed in a perfectly tailored charcoal suit. The rebellious edge in his brow had settled into a profound, calm depth, surfacing as that signature, possessive tenderness only when his eyes met mine.

And I was nearing the completion of my PhD at Tsinghua.

After the ceremony, we slipped away from the crowds and instinctively headed toward the place where it all began—the rooftop balcony above the old laboratory.

"The lock still hasn't been changed." Lu Shaodong pulled a thin wire from his pocket and expertly fiddled with the mechanism.

With a soft click, the door swung open.

The evening breeze rushed to meet us, carrying the humid scent of an early Nanshi summer. We stood side-by-side on the territory where we had once shared a stolen kiss.

"Yin," Lu said, looking down at the students running on the track, his voice low. "When I used to stand here, I felt like the world was a giant cage. I thought I was destined to struggle in the mud forever. Until I met you."

I turned to look at the perfect profile of his face. The setting sun traced his features in gold, making him look like a hero who had finally returned from a long campaign.

"You were the variable that crashed into my lab," I said softly. "Without you, I might have just been a machine that solved equations, never knowing that the world had heartbeats as well as formulas."

He turned to me abruptly, reaching into the inner pocket of his suit to pull out a black velvet box.

He didn't kneel; instead, he stood with an equal, powerful posture, looking me straight in the eye. The box opened to reveal not a massive diamond, but a ring crafted from a unique aerospace composite material. Engraved on the inside was a string of tiny physical coordinates.

"Those are the coordinates of the first time we looked at the stars together," he explained, a rare hint of nerves in his voice. "Yin, I’ve studied all the laws of physics. The law of entropy says the universe will eventually slide into chaos and death. But I’ve found that in our system, that law fails."

He picked up the ring, his gaze so intense it felt as though it could melt me.

"Because there is a force that doesn't weaken with distance or fade with time. It is deeper than gravity and swifter than electromagnetism."

"Marry me. Be the only, eternal constant in my life."

I looked at him, my vision blurring with tears. I remembered our first kiss on this balcony, our reunion under the first snow in Beijing, and our bond forged in life and death at the peak of Mount Dongling.

The entire past converged into a perfect closed loop at this moment.

"Lu Shaodong," I said, reaching out my hand and letting him slide the ring—warm from his touch—onto my finger. "Physics can't prove 'forever,' but I can."

He pulled me in by the back of my head, sealing my lips with his.

Below the balcony, cheers erupted from the students on the playground, and the crisp school bell rang from the distance. It was the echo of youth and the start of a new chapter.

In a world full of variables, we had finally found our unique, eternal gravitational field.

THE END

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