"How much?" Wu Zheng asked.

  They were sitting in the corner of their rented room, the remains of Wu Zheng's dinner (a soup that had no right being as good as it was, made from ingredients Chen Xi could not identify and did not want identified) cooling between them.

  "At our typical proximity, over the six weeks in the Silted Bones, I estimate I drained approximately three to four percent of your total cultivation recovery. Not enough to cause harm, but enough to slow your progress measurably."

  "Three to four percent."

  "Yes."

  "Over six weeks."

  "Yes."

  Wu Zheng was quiet for a long time.

  The room's single window let in the noise of Jianzhou at night: distant laughter, a musician practicing scales, the muffled percussion of a formation being tested somewhere in the Arena district.

  "I spent seventy-three years in that graveyard," Wu Zheng said.

  "Seventy-three years eating moss and talking to bones. You got me out. You gave me a reason to be alive. And you're telling me that your method stole four percent of my Qi."

  "Yes."

  "That's the worst apology I've ever heard. You sound like you're presenting a paper."

  "I am, essentially, presenting a paper. The data is clear. The conclusion is that my method has a flaw I didn't anticipate, and the flaw caused harm to someone I—"

  He stopped. The word he wanted to use was not a word he used.

  It implied attachment, obligation, emotional investment — all the things he had filed away in the part of his mind where he kept the grief about Elena and the coffee machine and the life he'd lost.

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  "Someone you what?" Wu Zheng asked, gently.

  "Someone I owe a considerable debt to. In the strict transactional sense."

  "The strict transactional sense."

  "Yes."

  Wu Zheng smiled. It was the kind of smile that contained an entire argument about the limitations of transactional models for describing human relationships, compressed into a facial expression because the old man knew that the argument itself would bounce off Chen Xi's analytical framework like a pebble off a wall.

  "I forgive the four percent," he said.

  "Now tell me: does this effect scale?"

  "Yes. Proportional to ambient Qi density and the cultivation level of nearby individuals.

  In the Silt, the effect is minor. In a denser environment — like Jianzhou during the Sword Conference, or the Second Stratum — it could be significant."

  "Significant how?"

  "In the Second Stratum, where Qi density is a hundred times higher, I could potentially drain a cultivator within fifty metres by ten to fifteen percent over a sustained period.

  Enough to destabilise an active technique. Enough to cause a cultivation deviation in someone at a critical moment."

  "Enough to kill someone."

  "Yes. Indirectly. Yes."

  "Then you need to fix it."

  "I know. The fix requires redesigning the core pressure differential to create a selective intake filter — only ambient, unattached Qi enters the vortex. It's mathematically complex and it will reduce my peak efficiency."

  "By how much?"

  "I estimate a drop from sixty-seven percent to approximately fifty-two percent. Significant but still far above conventional methods."

  "Do it."

  "I will. After the tournament."

  "Why after?"

  "Because the fix will take weeks to implement, and the tournament starts in four days, and I need the current efficiency to compete." He paused. "And because Li Wei has noticed."

  "Noticed what?"

  "The drain. He doesn't know what it is, but he can feel it. His cultivation has been fluctuating when I'm nearby, and he's not stupid. He's going to figure it out, and when he does, his grievance against me will be legitimate."

  Wu Zheng set down his cup. "You're entering a tournament against a man whose Qi you've been accidentally stealing."

  "Yes."

  "And you don't see how this might be a problem."

  "I see exactly how it's a problem. That's why I'm telling you. I need you to understand the complete picture because I am not, apparently, reliable at predicting the social consequences of my technical decisions."

  Wu Zheng sighed.

  It was the sigh of a man who had spent enough time with Chen Xi to know that self-awareness, in this particular individual, did not reliably translate into changed behaviour.

  But it was a start.