The dice came to rest on the corner of the table, with five points facing up.

Chen Hao's hand was still hanging in mid-air, about to reach for it, when Nana spoke first: "The energy reserve alarm has been triggered."

He froze, slowly withdrawing his hand. "Huh?"

The control panel screen lit up, and a red curve climbed upwards. "Current daily heating energy consumption has increased by 12%. Based on the current fuel reserves, it can last for another 28 days."

"No... we just finished playing chess?" Chen Hao frowned. "I haven't even washed the screws yet."

“The weather model has been updated, and the cold wave cycle is expected to extend by more than fifteen days.” Nana’s voice remained the same, but her tone was like a radio program suddenly turning off its background music. “I recommend that the Level 2 energy reserve plan be activated immediately.”

Chen Hao sat motionless in his chair, staring at the ceiling for a few seconds, then suddenly slammed his hand on the table and stood up. "Alright, let's do it!"

He turned around, opened the tool cabinet, pulled out a saw, and tore out a few insulated oilcloth bags, muttering, "The wood has to be dry, the coal has to be big and burn well, and the sled can carry as much as it can."

“The collection route has been planned.” Nana pulled up the map. “There are three fallen trees at the edge of the forest that can be directly collected. There are exposed lignite seams on the southern slope of the old mining area, which are suitable for short-term mining.”

"Your brain is hotter than a furnace." Chen Hao put on his winter coat. "Come on, while I still have the energy."

The snow outside was ankle-deep, the wind wasn't strong, but it was bitterly cold. The sled chugged forward, its wheels squeaking through the snow. Chen Hao sat in front, holding the rope, while Nana checked the equipment list from the back.

"The saw is intact, the pickaxe is undamaged, and the tarpaulin bag is sealed properly." She checked each item one by one. "The estimated operation time is four hours."

"Stop reading it, it sounds like a deathbed message." Chen Hao shook the reins. "We're going to collect firewood, not to hold a funeral."

Upon reaching the edge of the woods, a leaning oak tree lay across the snow, its roots sticking out as if it had been forcibly uprooted. Chen Hao walked over and kicked it. "Hey, isn't this a freebie?"

He took out the saw and was about to start when Nana said, "It needs to be secured."

“I know.” He bent down and pulled two metal strips from under the sled; they were made from springs from a scrapped car. “Take a look.”

He wedged the metal strip into the middle of the tree trunk, tightened the bolts, and formed a makeshift support. He sawed a few times, and sawdust flew out, landing on the snow like crumbs of biscuits.

"Efficiency increased by thirty percent." Nana stood beside her taking notes, "Saving physical energy."

“That’s right.” Chen Hao said, panting. “I may be lazy, but I’m not stupid.”

After sawing off a section, he dragged it to the sled and fastened it with a click. After repeating this seven times, the hardwood piled up to a bulge.

"A total of 420 kilograms of dried hardwood," Nana reported after scanning. "Next step: head to the mining area."

On the way, Chen Hao rubbed his hands together and breathed on them to warm them up, saying, "If the weather had warmed up earlier, we wouldn't have had to suffer like this."

“Weather is beyond our control,” Nana said, “but we can prepare.”

The mine was on the back side of the hillside, where the wind had picked up noticeably. A patch of dark brown rock, interspersed with shiny grains, was exposed on the ground.

"Is that coal?" Chen Hao squatted down and touched it. "It feels quite rough."

“Lignite has a medium calorific value and is suitable for mixed combustion.” Nana marked five mining points with thermal imaging. “It is recommended to prioritize mining shallow areas.”

Chen Hao swung the pickaxe down, and a spark flew. He shook his wrist. "This thing is much more tiring on the arm than playing chess."

Pickaxe after pickaxe, the rubble crumbled, and chunks of coal tumbled down. Nana used tweezers to clean out the impurities and then packed them into tarpaulin bags. After six bags were full, she redistributed the weight to ensure the sled was balanced.

"Total weight 680 kilograms," she said. "Loading complete."

Chen Hao slumped down on the snowdrift, saying, "I feel like I'm turning into coal, so black and heavy."

"Your body temperature is normal." Nana handed her a bottle of water. "Replenish your fluids."

He took a swig, wiped his mouth, and said, "Let's go back. If I stay any longer, I'll really freeze into a fossil."

The return journey was along a gentle slope and was initially quite smooth. Halfway there, the road surface turned icy, and the sled suddenly slipped, with the front wheel veering off course by half a meter.

"Damn it!" Chen Hao jumped off the back of the car and used his ice axe to dig a hole in the ground. "Hold on!"

Nana adjusted the angle of the traction rope, distributing the power to both sides. The sled slowly straightened and continued moving forward.

"We almost crashed just now," Chen Hao said, catching his breath as he returned to his seat. "Next time, we'll bring snow chains."

“It’s been added to the improvement list,” Nana nodded.

Back at the storage area outside the base, the two untied the ropes. The wood and coal sacks were neatly stacked under the rain shelter.

"The total amount collected this time is 1,100 kilograms." Nana entered the data. "Based on the existing inventory, the heating period is expected to be extended to 47 days."

Chen Hao patted the dust off his hands. "That's about enough. At least we can hold out until someone remembers we're still alive."

"Next, we will implement redundant thermal energy storage." Nana walked towards the solar collector area. "We will absorb heat during the day and store it at night, operating on two parallel lines."

The sun hung in the sky, its light as weak as a light bulb about to run out of power. The surface of the solar collector was covered with a thin layer of snow, and the reflector was not deployed.

"The efficiency is only forty percent of the design value." Nana checked the readings. "It must be optimized."

She activated the backup reflector array, turning each panel one by one to face the sky. Chen Hao climbed onto the platform and laid the black stone slabs on the surface of the heat collection area.

"The darker the color, the better?" he asked.

“The absorption rate is higher,” Nana confirmed. “The temperature rise rate has increased by 22 percent.”

They stayed there for six hours. The water tank temperature slowly climbed, eventually increasing by eleven degrees Celsius.

"Meets short-term emergency standards," Nana noted. "It can support an additional eight hours of heating in the core area."

"What if there's a power outage?" Chen Hao asked, wiping his sweat.

"Activate the nighttime heat storage mode." She opened the virtual energy management system, "simulating off-peak electricity pricing periods, slowly heating the ceramic heat storage bricks."

The system starts running, and the indicator light changes from red to yellow.

"How long can these bricks stay hot?" Chen Hao touched the outer shell.

"It can release 70% of the heat within 48 hours," Nana said. "That's enough to cope with a sudden supply disruption."

"That sounds plausible." He grinned. "This isn't just being prepared, it's like welding the umbrella shut in advance."

“The metaphor isn’t accurate,” Nana said, looking at him, “but the intention is understood correctly.”

As darkness fell, the two returned to the storage area. The fuel wasn't fully stored; only half had been unloaded.

Chen Hao picked up a piece of wood and carried it inside, but then turned back at the door. "Hey, do you think we'll end up in textbooks if we work this hard?"

“The probability is less than 3.7 percent,” Nana replied.

“I just said it offhand,” he shrugged. “Anyway, we’ll live one day at a time. The longer we can keep the fire burning, the less we’ll freeze.”

He bent down and picked up the second load, his footsteps making a dull thud on the snow.

Nana stood still, the optical lens sweeping across the piled-up fuel, then turning to the distant horizon.

The wind stopped.

Her voice rang out.

"We need to add protective masks for the next collection."