I'm going to preface this by saying I know very little about Attack On Titan. What I do know is that a sword with a gun-shaped handle and detachable blade is all kinds of awesome, even if not terribly practical in a fight, against say, anything not Attack On Titan-related. That didn't stop one fan from crafting his own sword, based on those featured in the show.
The video here is a good 15-minutes long and narrated entirely in Japanese, but it does feature the weapon being used to chop up vegetables and threaten what appears to be an air-conditioning unit. It also has a walk-through of its construction via sketches, CAD and eventually milling.
A blog post by the creator contains a few more details, though a Google translation doesn't make anything particularly clear. For example, a manufacturing cost of 500,000 yen is mentioned ($5250), which seems a little on the expensive side. Or not.
If anyone out there can read Japanese, please feel free to enlighten us!