This is a Vortex Cannon used by Karakuri for self defense. It fires a burst of Compressed air in a form of a ring to know anyone off their feet.
You might say that this is way too big and cumbersome to carry around. And yeah you are right! But, Karakuri doesn't have to carry it around, he only has to carry around the blueprints. You see he only needs metal and the blueprints to make this weapon.
Karakuri can in theory rip out a "Stop" sign from the sign of the road and as he is holding it he can rearrange all the atoms in the signpost into this gun in a matter of 2 seconds and the weapon is ready to fire. The only problem is that moving around so many atoms in such a short period of time makes the product extremely hot for a short period of time.
The wheel in the back holds capsules holding a nitrogen based explosive used to pressurize the air and push it out the barrel. Why nitrogen based? Well 70% of what you breathe is Nitrogen, of course Nitrgoen gas is not flammable or explosive so Karakuri must change the molecule to make it explosive, the resulting fuel has bout 50% of the energy to volume ratio of gasoline.
Effective range: 200 m
Rate of fire: 60/min