A fuse is the part of an explosive, pyrotechnic device, or military munition that initiates it's function.
According to the Giyoshu military manual, waterproof fuses can be created by grinding camphor up and mixing it in two bowls of water, if it tastes pungent, a fuse would be soaked in it and then dried. Or soak a fuse in white lead for seven days. Another way to create waterproof fuses is by soaking them in the liquid used for dying teeth without the sumac nutgall or by by braiding a fuse out of old cotton cloth and boiling it in saltpeter, pine resin, and water. The fuses would the be dried.
Alternatively, fuses could simply be soaked in lye from the camellia plant or straw and dried. An alternative to fuses could be a dried head of a cattail plant or by exposing the stems of a giant butterbur plant in the sun and braiding them.