Half the oil lamp's wick had burned black, and its flame flickered. Rinto idly nudged it with the tip of his carving knife. Sparks scattered onto the rough paper covered in patterns. He raised a hand, glanced at them, and paid them no mind. The charcoal pencil between his fingers kept moving across the paper.
There was barely any blank space left on the paper. Both sides were filled with meridian channels. Some had been crossed out halfway through with a sweeping X; others had dense parameters marked in their corners, revised again and again. Even the gaps were crammed with figures for flow speed, damping, and pressure differential. He had lost track of how long he had spent in the laboratory. Outside the window, daylight gave way to darkness, then darkness to daylight, but he remembered none of it. All he remembered was refilling the lamp three times, and the discarded paper on the floor had piled above his ankles.
The phrase "use the body as a vessel," painstakingly extracted from that half-scroll fragment, lodged in his mind like a nail. He had spent more than ten days pursuing the dead end of anchors. Now he was scrapping it entirely and starting over, turning all his meridians into a circulating network capable of holding natural energy rather than forcibly locking it down with countless tiny anchors.
He did not methodically draw up a perfect blueprint first. For his first attempt, he chose only the simplest stretch of meridians in his left forearm. Chakra followed the modified channels, circling the closed loop again and again. The damping structures kept its speed firmly controlled, without disorder or eddies. He maintained the circulation without stopping, letting chakra turn through his forearm for nearly ten minutes. Only when there was still no tingling in his fingertips did he relax his shoulders a fraction and gently set the carving knife on the stone workbench. Its sharp clink sounded especially clear in the oppressively silent laboratory.
The logic worked.
But the meridians in his forearm accounted for less than a tenth of those in his entire body. Expanding it throughout his body meant dealing with the main meridians in his chest and abdomen, the branches in his limbs, and the junctions around his shoulders and neck. Their widths differed, and the natural differences in chakra flow speed could reach twofold. Simply copying the forearm's structure would not work.
He did not rush to expand it throughout his body. Hunched over the stone workbench, he calculated parameters and revised damping structures section by section against the full-body meridian diagram he had drawn. The charcoal pencil never stopped moving. When he reached the meridian junctions, he got stuck. Its tip lingered against the paper, poking several black holes through it. Where a channel split in two, both speed and pressure changed. Fixed damping could not handle that. A flow that was steady one second could develop eddies the next.
He tried three versions of the structure, working them through on paper first, but the more he revised them, the messier they became. Either the pressure differential at the junctions went uncontrolled, or the flow in the main meridians slowed, doubling the energy cost of the entire circuit. Irritated, he flung the pencil onto the table and rose to pace around the laboratory, his footsteps rustling through the crumpled paper on the floor.
When he reached the wall, his gaze passed over the rubbing of the Martyrdom Sealing patterns he had pinned there earlier. He had casually taken it while dismantling the seal. Its responsive patterns did not control pressure at individual points; the entire array adapted to the pressure.
His footsteps stopped abruptly.
His earlier idea had been to add an adaptive valve to each section of meridian to control flow speed and adjust damping. But what if, instead of controlling individual points, the entire channel structure made minute adjustments in real time according to the chakra's pressure and speed? Like the Martyrdom Sealing array, which did not rely on a single core to control everything, but let every section of its pattern adjust itself.
The thought pierced the knot that had blocked him for so long like a needle. He spun and rushed back to the stone workbench, grabbed fresh paper, and sent his charcoal pencil racing across it. He replaced the separate damping structures in each section with a responsive structure linking every channel, allowing each part of the circuit to adapt automatically to pressure differentials and flow speeds as neighboring channels changed.
By the time he finished revising the entire circuit, the paper was densely covered. He raised a hand to rub his eyes and only then noticed that it was already pitch-black outside. The wavering lamp flame blurred his vision, and his empty stomach cramped. Only then did he remember that he had eaten nothing since morning.
The dry flatbread he had brought back earlier lay beside the table. He picked it up and bit into it. The hard, dry wheat flour scraped painfully down his throat, and he washed it down with cold water from the dipper. He finished it in a few bites. Crumbs fell onto the diagram, and he brushed them aside, paying no attention even when he smudged half a line of parameters. Then he closed his eyes, settled his mind, and activated the circulation throughout his body.
Chakra began flowing along the newly modified channels.
For the first half minute, it was indeed stable. The responsive structure kept the flow speeds in the main and branch meridians even, smoothing out the pressure differentials at the junctions. None of the anticipated eddies appeared. Something had just stirred in him when he tried adjusting his breathing. That single adjustment made the meridians in his chest contract slightly, instantly changing the flow speed in the main meridians of his chest and abdomen. The responsive structure lagged half a beat behind. Eddies immediately formed at the junctions around his shoulders and neck, and the chakra fell into chaos.
He immediately dispersed the chakra, but he was still too late. The turbulence struck his meridian walls, drawing a muffled grunt of pain as his back went rigid. He braced himself against the stone workbench for a long time before the stabbing pain racing through his meridians subsided.
It still did not work.
The responsive structure's linked reactions could not keep up with changes in his body itself. Breathing, heartbeat, even slight muscular contractions altered the state of his meridians. The linkage logic he had designed was still too idealized to follow his body's changes in real time.
He neither swore nor smashed anything. He merely clenched his back teeth, sat down on the stone stool, and stared at the diagram, running his fingertip repeatedly over the shoulder-and-neck junction where the problem had occurred. He revised the linkage logic and added predictive compensation, factoring the meridian changes caused by breathing and heartbeat into the parameters in advance.
Those revisions took most of the night. The lamp ran dry. He replaced the wick in the dark and lit it again. Only when lamplight spread across the stone workbench once more did he notice that the charcoal pencil had rubbed the skin off his fingers at some point. Blood mixed with charcoal dust had smeared all over the diagrams. He ignored it and kept revising.
Near dawn, he finished the second version of the full circulation structure.
He did not test it immediately. Leaning against the rock wall with his eyes closed, he went over the logic of the entire channel network, every section's parameters, and the linkage triggers three times in his mind. Only then did he take a deep breath and restart the circulation.
This time, it was much steadier. Chakra flowed smoothly through the meridians throughout his body. Even when he deliberately changed his breathing and tensed his muscles, the responsive structure kept pace. The circulation did not fall into disorder, and no eddies appeared. It ran steadily for over twenty minutes, with chakra consumption remaining within controllable limits.
He had more or less overcome the problem of a stable internal circulation.
But that was only the first step. No matter how steady the circulation was, it was useless if it could not hold natural energy.
He did not rush to draw natural energy into it. First, he stopped the circulation, sat on the stone stool, and stared blankly at the diagram for a long time. The previous closed circuit was a sealed water tank. Any natural energy poured into it, no matter how little, would alter the density and pressure of the entire system. However stable the channels were, they could not withstand the impact of external energy.
The fragment read, "Take in the tide as it comes; cease as it recedes." An intake without a sluice for discharge would not do.
He picked up the charcoal pencil and cut several openings into the closed circuit he had just drawn. He added dedicated energy intake channels to guide natural energy evenly into the circulation rather than letting it burrow haphazardly through his pores. Beside the main meridians, he added buffer sections where natural energy and his own chakra could undergo initial fusion before entering the main circuit, avoiding a direct impact on the whole system. Most importantly, he added controllable overflow channels. If fusion became unbalanced or energy overloaded, excess natural energy could immediately escape through them instead of wrecking the entire circulation.
With those changes, the formerly complete closed circuit became a semi-open system. The channel diagram had been altered beyond recognition. Even he could no longer remember how many versions he had scrapped and rebuilt.
The first time he drew in natural energy, he dared admit only an exceedingly fine strand, thinner than a hair, guiding it inward through the intake channels. It entered the buffer section, fused a little with chakra, then entered the main circuit. The entire system remained orderly and extremely stable.
He tried increasing the intake. Before he had raised it even ten percent, the buffer section's fusion speed fell behind. Natural energy that had not fully fused rushed into the main circuit, instantly disrupting the energy balance. The responsive structure adjusted frantically, but still could not keep up with the changing energy density. The entire circulation fell into chaos at once, chakra and natural energy rampaging through his meridians.
Rinto immediately activated the overflow channels while doing everything he could to disperse all the chakra in his body. But the uncontrolled energy still surged into the branch meridians. Pain doubled him over. His hands clawed at the edge of the stone workbench, knuckles white, teeth grinding. Sweat dripped from his forehead onto the stone slab, spreading into a small damp patch. He did not even have the strength to make a sound.
It took nearly half an hour before he could straighten up, and his forearm muscles were still twitching uncontrollably. He did not inspect his injuries. His first reaction was to pick up the charcoal pencil, circle the buffer section on the diagram, and draw a heavy X over it.
The fusion speed could not keep up, and the rhythms of intake and overflow did not match. It still collapsed.
He spent the next two days on this. He revised the buffer sections' structure, adjusted the widths of the intake channels, and matched the opening and closing thresholds of the overflow channels. Every test ended in collapse. At best, it lasted five minutes. At worst, everything fell into disorder the moment natural energy entered.
Discarded drafts piled higher on the floor, and his injuries multiplied. Some were meridians split by chakra turbulence; others were cuts from broken stone during backlash. He simply rinsed them with povidone-iodine and went straight back to revising his diagrams. One collapse was particularly severe. The overflow channels failed to open in time, and natural energy surged into his lung meridian. He coughed for a long time, bringing up a little blood. He wiped his mouth and still did not stop.
It was not until his third revision of the buffer sections that he embedded the nature-fusion logic from Dynamic Reconstruction into them. Instead of passive vessels, the buffer sections became active fusion anchors, guiding natural energy and chakra to fuse in step.
When he tested it again, it was finally different.
Natural energy entered through the intake channels, and the buffer sections steadily received it, fusing it bit by bit before feeding it into the main circuit at an even rate. Excess energy drained smoothly through the overflow channels. The entire semi-open circulation turned as steadily as a waterwheel worn smooth.
One minute, five minutes, ten minutes, twenty minutes.
There was no stabbing pain in his meridians, no turbulence, no imbalance. Physical energy, spiritual energy, and natural energy fused steadily along the circuit. Senjutsu chakra accumulated bit by bit and flowed through his meridians, a faint, slightly cool aura lingering around his fingertips. Without a medium, without carving anchors beforehand, it remained steadily under his control.
Rinto slowly stopped taking in natural energy and maintained the circulation for another ten stable minutes before withdrawing his effort entirely. When he opened his eyes, his vision was somewhat blurred from staying awake too long. He looked down at his hands, then at the diagrams on the table, altered beyond recognition, and let out a long breath that trembled slightly.
The path was open.
But his happiness did not last long. He did not even sit down to catch his breath before picking up the charcoal pencil again. In that test, his natural energy intake had been pitifully slow, and the fusion rate had been below thirty percent. Maintaining it for twenty minutes had consumed nearly thirty percent of his own chakra. He was still far from Barehanded Senjutsu that could be used in actual combat and maintained for long periods.
He marked the diagram with a dense list of problems: low intake efficiency, insufficient fusion rate, excessive circulation costs, too much energy wasted through the overflow channels... He wrote them clearly, one by one.
The lamp flame began wavering again. Its oil was nearly gone. Morning light came through the vent from outside, falling across his hands, covered in charcoal dust, bloodstains, and sweat. He did not even lift his eyelids. The charcoal pencil had already touched the paper as he began revising the next optimized version of the structure.
From beginning to end, he never heard the waves or the cries of seabirds outside.