Tsuranuki Zutsu

The Tsuranuki Zutsu (ツラヌキ筒) is a weapon created to pierce the Kabane's iron hearts more efficiently than conventional steam weaponry, invented by Ikoma and Takumi. A combination of high pressured steam injected into a cartridge of gunpowder creates a needle-like explosive reaction that can bore through both cage and heart of a Kabane with ease, although at the cost of its nearly nonexistent range; the gun has to be fired at point blank, something that few people dare attempt and cost Ikoma his humanity. The main concept came from a simple steamsmith's rivet gun, possibly upscaled and weaponized to the point it could be used against Kabane.

It is unknown at the time if both worked on the project together or if Ikoma was the original gunsmith while Takumi helped him brainstorm, but there seems to be only a single one made as of yet. However, given it could of been made by just two steamsmiths, the production of additional units might be possible given the right materials.