Kilahuea

A gunpowder-charged pile bunker. Can bring down castle walls.

Pile Bunker

The piston is driven by a gunpowder charge, stops short of flying out due to wide stop at the end. However, that stop can be collapsed into the piston for a ranged attack. It needs to be collected again before it can be used, though.

Hardened steel spike, plated "gauntlet" with leather straps and a wrapped handle.

~40 lbs

The piston is housed in a casing that connects to a set of straps. There is a strap for the arm and a handle to hold onto, can be put on either arm. The piston is a very large spike, and the powder charge is specifically measured out so that it won't break upon use.

Can be recalled to and from the Hoard at any time.

The Kilahuea was made as a precautionary tool. There may be a time where Earthbending isn't enough to pierce something, whether it be scales or some human-made contraption. There were times where Yama thought his weapon building habit was getting a bit out of control, but then he realized that he had too much fun using them to stop. It was obsessive, but it worked.