The journey back to Liyue Harbor was a strange and silent procession through the clouds. Xianyun, as always, carried Ren with an effortless grace, his small form secure in her arms. Flying behind them, keeping a steady, watchful distance, was Shenhe. She moved with the same fluid power, her silver hair trailing behind her like a comet's tail. Cradled in her arms was the wooden heater, a box of future warmth held by a woman who radiated a perpetual, personal winter. The juxtaposition was not lost on Ren; it was a perfect, silent encapsulation of his new, bizarre, and wonderful family.
Their arrival at the house on Feiyun Slope was met with a gasp of pure, unadulterated joy. Ganyu, who had been home that day, casually watching the sky from the garden every spare moment, practically flew to the gate the moment she realized they were here.
"Master! Ren! You're back!" she cried, her voice thick with relief and happiness. She immediately enveloped Ren in a tight, loving hug the moment Xianyun set him down. Then, her eyes fell upon the silver-haired figure standing silently behind them.
"Shenhe?" Ganyu whispered, her eyes wide with surprise. She knew of her fellow disciple, of course, but their paths had rarely, if ever, crossed. One was bound to the heart of the city's bureaucracy, the other to the desolate, monster-infested peaks.
"Ganyu," Shenhe acknowledged with a single, curt nod. There was no warmth in the greeting, only a statement of fact.
An awkward silence fell as the two "sisters" regarded each other. Ganyu, the embodiment of gentle diligence, and Shenhe, the incarnation of cold, lethal focus.
"It is… good to see you," Ganyu said finally, offering a slightly flustered but sincere smile. "Please, come in! You must all be tired."
The awkwardness melted away as the focus shifted to the heater. Shenhe carried the device into the main living area and set it down with a care that seemed at odds with her frigid demeanor. Under Ren's careful direction, they positioned it in a corner of the room, where its warmth would radiate out towards the comfortable seating cushions.
The rest of the day passed in a pleasant buzz. Ganyu doted on Ren, plying him with snacks and asking a million questions about his time on the mountain. Shenhe remained largely silent, a beautiful, intimidating statue in the corner of the room, her glacial eyes observing everything, her presence a constant, silent promise of protection.
As evening descended, a familiar chill began to creep into the house. It was time.
With a sense of ceremony, Xianyun knelt and slotted a fresh electro crystal into the device. Ganyu and Ren sat together on the large couch, watching with bated breath. Xianyun turned the dial.
The soft hum of the fan filled the room, a gentle, promising sound. A warm, violet glow emanated from the vents, and then, the heat began to flow. It was a slow, creeping warmth that pushed back the evening chill, chasing the cold out of the corners and wrapping the room in a cozy, comfortable embrace. It was a tangible, physical manifestation of home.
Ganyu let out a soft sigh of pure contentment, pulling Ren a little closer, though the room no longer required it. Shenhe, still standing by the wall, tilted her head, a flicker of something unreadable—perhaps curiosity, perhaps confusion—in her icy eyes as she felt the unnatural warmth on her skin. Xianyun watched the scene, a profound, quiet satisfaction on her face. Her strange, fractured family was gathered together, warmed by a hearth born from her youngest's impossible mind.
It was Ren who broke the peaceful silence.
"It's good," he said, his voice thoughtful. "But it's not perfect."
Ganyu looked down at him, confused. "What do you mean, Ren? It's wonderful!"
"The housing is too big," he explained, his gaze critical. "We can make it more compact. And the wood… it gets a little warm to the touch. It's not dangerous, but it could be better insulated. We should add a layer of treated ceramic on the inside to protect from the heat, and maybe a rubber-like sealant around the crystal's door, to avoid any chance of a static shock."
He looked up at Xianyun. "And the blueprint is a mess. It's my working draft. Before we show this to anyone, I need to make a proper one. A master copy that any skilled craftsman can read and understand, with notes on materials and assembly. We have to wait a little longer before we present this."
His tone was firm, the mind of the engineer overriding the contentment of the child. Xianyun nodded in complete agreement. "Your assessment is correct. Optimization is a crucial step. Haste would be illogical."
Ren then hopped off the couch, ran to the small satchel of drawing supplies Ganyu had given him, and pulled out a fresh, rolled-up sheet of paper. He walked back and presented it not to Ganyu, but to Xianyun.
"But while I'm working on the heater upgrades," he said, a familiar spark of invention in his eyes, "you could start on this, Master. If you want."
Xianyun took the scroll and unrolled it. Ganyu leaned over to look. It was another blueprint, just as detailed and precise as the first. But the design was different, and the central crystal was labeled not 'electro', but 'cryo'.
"What is it?" Ganyu asked, her voice a whisper of awe.
"It's a refrigerator," Ren explained. "It works on the same principle as the heater, with a fan pulling air through. But instead of an electro coil, it uses a cryo crystal to cool the air. The cold air is trapped inside this insulated box, and it keeps things inside very cold."
He pointed to a drawing of a fish and some berries inside the box. "It can be used to keep food from spoiling. Fish from the wharf, meat, vegetables, even medicine. It will let people store food for much longer."
Xianyun's eyes scanned the blueprint, her brilliant mind already dissecting the mechanics. "I see you have omitted the regulator dial. Why?"
"Because we don't need to control the cold," Ren said, the logic clear and simple in his mind. "With the heater, we couldn't use a pyro crystal because it's always on at maximum heat, and that would be uncomfortable or even dangerous for people. We needed to regulate it. But the refrigerator's job is just to be as cold as possible to preserve food. The raw, untamed power of a cryo crystal is exactly what we want. No need for control, just pure, constant cold."
The simple, elegant reversal of the core problem left Xianyun speechless for a moment. He had not just solved one problem; he had used the limitations of their world's elements to his advantage to solve a second.
He then turned, his expression softening as he looked at Ganyu. "I want to stay here for a while, big sister. In the Harbor. I can work on the new heater blueprints here, and… and I miss you when I'm on the mountain."
Ganyu's heart felt like it was going to burst. She pulled him into a hug, burying her face in his hair. "Oh, Ren. I miss you too. Of course, you can stay! Stay as long as you want!"
Ren looked over Ganyu's shoulder at his Master. "You can take the new blueprint back to Mt. Aocang, Master. You can start building the refrigerator if you like. I'll be fine here with big sister Ganyu."
A new plan had been forged in the warmth of their new hearth. The family would split once more, but this time, it was not a sad departure. It was a new phase of their shared project, a division of labor born of love and a shared, brilliant purpose.