The creation of the hoverboard was a testament to the seamless, practiced synergy that now existed between Ren and Xianyun. Armed with the hard-won knowledge from their previous inventions, they worked with a speed and efficiency that was breathtaking.
The core challenge was, as Ren had predicted, the propulsion system. Xianyun, with her mastery of materials, forged the propeller blades from a lightweight but incredibly durable metallic alloy, shaping them to the perfect aerodynamic curve Ren had designed. The small, high-torque electric motors were a refined version of the one used for the heater's fan, miniaturized and made far more powerful.
The true genius of the design, however, lay not in the mechanics, but in the control system. It was here that Ren's otherworldly knowledge and Xianyun's adeptal artistry merged into something truly magical.
Instead of complex gyroscopes or steering columns, the board was controlled by the rider's feet. Xianyun, guided by Ren's schematics, inscribed a series of intricate, glowing runes directly onto the surface of the board where the rider would stand. These were not the profoundly complex, power-infused sigils of a true adeptal device. Ren had designed them to be simpler, a form of mechanical circuitry disguised as art. They were patterns that, when forged into the conductive surface of the board, would react to minute shifts in pressure.
"It's a mortal invention," Ren had insisted. "The runes can't be magical. They have to be something a skilled blacksmith can learn to recreate."
The result was an intuitive, almost telepathic, control scheme. Pressing down with the ball of the foot would increase power to the forward propellers, moving the board forward. Shifting weight to the heel would engage the reverse thrusters. Tilting from side to side would create a differential in thrust, allowing for smooth, graceful turns. It was a system that translated the rider's own sense of balance directly into flight.
Safety was their other paramount concern. Xianyun designed a set of elegant, low-profile latches that would gently but firmly secure the rider's feet to the board, preventing them from slipping off. And deep within the power core, she inscribed a single, crucial adeptal rune. It was a height restrictor, a safety measure that would prevent the board from ascending more than ten feet off the ground. "A fall from a greater height," she had stated with grim finality, "would be… problematic."
After a little over a week of intense, focused work, it was ready.
It sat on the flat peak of Mt. Aocang, a sleek, dark-grey platform about the length of Ren's own body. The control runes glowed with a soft, inviting blue light. Shenhe stood nearby, a silent, watchful guardian, her expression as unreadable as ever.
"The theoretical and practical components are aligned," Xianyun announced, her voice full of a quiet, scholarly pride. "The prototype is complete. It requires a test pilot."
There was no question as to who that would be.
Ren stepped onto the board, his small shoes settling perfectly into place. The latches clicked softly, securing his feet. He took a deep, steadying breath, his heart pounding a rhythm of nervous excitement. He looked at the control runes, then at the open sky before him. He shifted his weight forward, just a fraction of an inch.
Whrrrrrrrrrrrrrrrrrr...
A low, powerful hum vibrated up through the soles of his feet as the propellers spooled to life. The hum grew into a smooth, steady whine, and the board began to tremble. He pushed down a little more.
And then, he was flying.
The board lifted off the ground with a smooth, effortless grace, rising a few feet into the air and hovering there, as stable as a rock. The feeling was indescribable. It was a sensation of pure, untethered freedom, a quiet, personal defiance of gravity.
A wide, joyous grin split Ren's face. He leaned forward, and the board surged ahead, gliding silently over the polished stone of the mountaintop. He tilted his feet, and it banked into a perfect, graceful turn. He leaned back, and it slowed to a gentle, hovering stop. It was as easy and as intuitive as walking.
Shenhe watched, her glacial-blue eyes tracking his every movement, a flicker of something—surprise? wonder?—in their depths. Xianyun observed with the proud, satisfied look of a master craftsman watching their creation perform its function flawlessly.
Ren grew bolder. He zipped back and forth across the peak, his messy, blue-streaked hair whipping in the wind he created. He did graceful figure-eights around the stone table, his laughter echoing in the thin mountain air. He was a small, joyful blur of motion against the serene, ancient backdrop of the adeptal realm.
He was not just an inventor anymore. He was a pilot. He had looked at the sky, at the world of the Anemo Archon, and had, through sheer ingenuity, created a small piece of that freedom for the land of stone and contracts. This was more than a machine; it was a promise, a first, soaring step towards a future where anyone, not just the adepti or the wind-gliding knights of Mondstadt, could touch the sky.