Bracelet-sized kua-tin breathing device grafted into Louis's bronchial tube to keep him alive.
Mordecai taken it from Loita's body after assassinating her, and it has sat in Carl's inventory ever since. When the surgical plan needs a way for Louis to survive on naiad lungs, Edgar asks for it. Carl digs it out and objects that it is far too small — the size of a large bracelet — and Edgar answers, "Not where we're going to put it."
During Louis's Surgery, Mordecai makes a slit in the bronchial and works the rebreather down into the flesh, sewing rapidly. Rosetta confirms that this is how these devices are actually designed, internal or external, and that Louis won't like it but it will work. With gills grown by a Water Breathing Scroll and stops jammed into the slits by Bucket Boy, the graft holds.
A tiny device roughly the size of a large bracelet, kua-tin make.
The implant that makes Louis's naiad organ transplant survivable.