The Tsuranuki Zutsu (ツラヌキ筒), or "Piercing Gun," is a weapon created to pierce the iron hearts of Kabane more efficiently than conventional steam weaponry, invented by Ikoma and Takumi.
The Tsuranuki Zutsu was designed and developed by Ikoma and Takumi and as of yet only a single one has been made. However, given that it has been made by just two steamsmiths, when provided with the right materials additional units could be produced.
Ikoma, assisted by Takumi, spent his free time building and testing the Tsuranuki Zutsu whenever possible. The main concept came from a simple steamsmith's rivet gun, upscaled and weaponized to the point that it could be used against kabane. Ikoma's goal was to pierce the iron cage surrounding a kabane's heart, which he attempted to replicate with a thick sheet of iron. After countless failed attempts, Takumi suggested Ikoma focus on a different area, which proved successful. However, when Aragane Station fell to kabane, Ikoma was forced to field test the Tsuranuki Zutsu on the nearest kabane. When he managed to lure one inside his home, he attacked it with the Tsuranuki Zutsu. It worked, successfully piercing the kabane's heart cage, but it had one fatal flaw: it required a point-blank range in order to function, which nearly cost Ikoma his life.
The Tsuranuki Zutsu is a close-range weapon. 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. Ikoma, the main user, is forced to use the gun at point-blank range in order to pierce a kabane's heart cage. He slams the tip of the barrel against the kabane's chest, over its heart, and pulls the trigger. Any farther away and it is unlikely the gun will pierce the cage. This could prove fatally dangerous to any human user, as Ikoma is often repeatedly bitten by kabane before he manages to kill it.
The Tsuranuki Zutsu uses a custom form of ammunition Ikoma calls "jet bullets," which may or may not involve iron nails. It is currently unknown as to whether Ikoma utilizes actual nails or simply needed the metal to create his own jet bullets. Jet bullets, according to Ikoma, produce more penetrating power than an ordinary lead bullet.
Unlike the steam guns wielded by the Bushi, the Tsuranuki Zutsu is miniaturized to the point that it does not require the portable backpack engines needed to use a steam gun.
After Ikoma lost his right arm, he welded the gun to the stump of his right arm and operated the trigger with his left. In Battle of Unato, it was removed and a prosthetic was installed in its place, allowing Ikoma to wield it normally again.