On the second morning on Uninhabited Island, Kanzaki Toru woke to the final sweep of white light from the lighthouse. Dawn had just crept over the sea beyond Tin Roof, and the rising June sun sliced through the sea fog, turning it into a thin veil of pale gold over the shrubs and the spring on the back slope. After settling naturally overnight, the water in the public backpack's filter had left a thin layer of mineral sediment at the bottom of the bucket. Ishizaki was already crouched beside the water source, using a folding trowel to widen the muddy banks by about a palm's width. He moved at least twice as slowly as he had yesterday while hacking through vines, but each scoop stopped at precisely the same depth.
Morishita Ran's body clock beat the alarm. By the time Kanzaki Toru stepped out of Tin Roof, she was already sitting beside her cot, organizing the communications log. She had projected every group's freshwater allocation sheet from the day before onto the only folding table in Tin Roof. Her finger rested on the six notes in the final column of Group 12's sheet—each allocation came with a reason. "The school's system has flagged our notes explaining the freshwater allocations as a 'model example of compliance,'" she said, looking up at Kanzaki Toru. Her expression was calm, but there was a trace of surprise in her voice. "The Shared Pool weighting starts counting toward our score as of this moment. Those arguments we had on the path yesterday about map coordinates and equipment weight were also counted toward our 'collaboration friction coefficient.' It's below the threshold, so our collaboration score automatically goes up by one level."
Kanzaki Toru took her tablet. The "Collaboration Score" field had turned green, with a line of small text beside it: "Current rating: B+, one level away from unlocking the task-supply crate." He handed the tablet back to Morishita and turned toward the doorway to tell the others.
Hamaguchi was making a third comparison of the water-testing strips. He simply nodded at the news and continued writing notes. Nomura used a highlighter to retrace the signal-loss circles on the paper map, then added a note beside the cliff coordinates: "Cliff face shows significant weathering. Recommend completing the climbing-gear wear assessment before Day 4." Shiina Hiyori sat on her cot, reading the Shared Pool appendix to the Old System. Her light chestnut hair was still loose, but she had already written out a complete calculation of the collaboration-score weighting for each unlock condition and pinned it above the iron lock on the task-supply crate. Yesterday, they had only examined the lock. Today, they knew the precise score threshold for every step. One more level, and they could open the crate.
At nine in the morning, the school sent the second day's task over satellite text. The task title was just four words: "Freshwater Crisis." Each group had to complete two assigned challenges by the end of the day. The first was to accurately measure the actual amount of freshwater all six members consumed over twenty-four hours and compare it against the estimated allocation plan they had submitted the previous day. An error of more than twenty percent would cost them collaboration points. The second was to find at least one new source of potable freshwater and test its quality on-site. At least four group members had to verify the data before it could be submitted. A red note at the end of the instructions read: "Water-allocation data collected for this task will be incorporated into the real-time weighting calculations for the Old System's Shared Pool provisions. The school's system will review every group's allocation rationale. Any allocations deemed inadequately justified will be automatically excluded from the Shared Pool."
Kanzaki Toru projected the task instructions onto the outer wall of Tin Roof. June sunlight streamed over the shrubs and fell across the rusted metal, casting the focused profiles of each group member into view. Ishizaki set down his trowel and wiped his forehead with the back of a muddy hand. His shoulders were still aching from hacking through too many vines the day before, but he didn't stubbornly bear it in silence like he used to at the gym. He simply leaned the trowel against a tree, went over to Kanzaki Toru, and bent to read the screen. "Freshwater consumption—we gave a reason for every bottle yesterday, but we never actually weighed what we used, one by one."
"Our estimates were just numbers on paper until today. Now the school wants us to reconcile them against real data." Kanzaki Toru shifted his gaze from the red note to the crate. "If the error in our actual consumption is under twenty percent, our collaboration score will rise to A, and the supply crate will unlock at the same time. Morishita, record how much water each person takes every time, with results precise enough to reproduce. Nomura, mark the coordinates of potential new water sources on the paper map. Hamaguchi and Ishizaki, form the sampling team and check them one by one. Shiina, verify that our allocation rationales comply with the Old System's provisions. I'll do the final check and submit everything."
The assignments were brief and clear. Everyone had found the one thing they needed to focus on over the next four hours. No arguments, no repeated confirmations. Yesterday's dispute over map coordinates on the path through the shrubs was like a stone pressed flat beneath their feet, now quietly embedded in the rhythm of their steps.
Ishizaki and Hamaguchi headed down the back slope. Downstream from the spring, they found a damp hollow hidden beneath ferns. Hamaguchi pushed the fronds aside and spotted a shallow layer of seepage at the bottom. The water was clear, but there was very little of it. It took a long time to fill even half a folding cup. Ishizaki crouched beside him, dipped a testing strip into the cup, and read the indicators against the color chart. Neither man wasted time on pleasantries. The only sounds were the soft touch of the strip against the water and the scratch of Hamaguchi's pen as he entered the test results on the record sheet.
At ten thirty, Kanzaki Toru gathered everyone in the center of camp to check the first comparison between actual consumption and the estimated plan. Morishita read the water records aloud, person by person. Some had overestimated by nearly ten percent; others had actually drunk less than expected between their two trips for water. The total error came to 6.7 percent, far below the school's twenty-percent limit. As she projected the result, the collaboration score on the terminal jumped—from B+ to A-. The seal on the crate in the corner of Tin Roof's wall came loose with a click, and its latch sprang open.
Inside the unlocked supply crate, three rows of equipment were neatly arranged: a folding solar still, three spare water-filter cartridges, a waterproofed satellite weather map, and an envelope sealed with red wax. Kanzaki Toru opened the envelope. Inside was a handwritten card in a lean, forceful script: "The Shared Pool is not a pool of equal shares. Every resource in it must be backed by a reason. An allocation without a reason will automatically fail you when you need your teammates most. This test is only about freshwater. The next one might not be. Sakagami."
He read the card aloud to the group, line by line. Ishizaki crouched beside the supply crate, his fingers lightly tracing the folding supports of the solar still. He didn't look as panicked as he had while grabbing a drainpipe to climb a wall. Instead, he hesitated, like he had the first time someone corrected his bench-press form at the gym. He looked up at Morishita Ran, sitting on the cot across from him. "Does Class A have a course called Fundamentals of Environmental Engineering?" Morishita nodded. "Then teach me how to use this, and I'll help divert the water from the back slope."
Hamaguchi and Nomura had already started using the satellite weather map to plan tomorrow's survey route. Shiina picked up Sakagami's card and turned it over. On the back, in even smaller writing, was another line: "For Group 12—the path you kept circling around at the same coordinates last year is one you didn't take today." She slipped the card into the outermost layer of the Old System reference sheet without showing anyone. In the notes column of the Shared Pool weighting chart, she added an "&" symbol.
By dusk, all the new water-source samples had been checked. Kanzaki Toru pressed the group confirmation button on the submission terminal. A message appeared on-screen: "Task completion: 100%. Collaboration score: A-. Shared Pool weighting bonus now in effect." Outside Tin Roof, Ishizaki and Morishita were crouched beside the solar still, adjusting the angle of its reflective surface. The first drop of purified water slowly slid into the collection bottle, joining the water from the back-slope spring in the same bucket. Hamaguchi wrote the final note of the day in the log: "Freshwater Crisis task complete. New source ID: NS-03. Water quality meets drinking-water standards. Recommend another microbial test before tomorrow's task begins. Recorded by: Hamaguchi Tetsuya." His neat handwriting sat beside the results Ishizaki had recorded that morning on the folding table.
Night fog rose again from the sea, and the lighthouse's white beam swept steadily over the Tin Roof. Tomorrow's task had yet to be announced, but the water in the Shared Pool was rising, one drop at a time.
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