This was neck and neck and….neck between three options; The Punisher, Wolfwood’s weapon from Trigun, Automail from FMA and 3D Maneuver Gear from Attack on Titan.
Automail are incredible prostheses that can be modified in all sorts of ways to add weapons and other capabilities. The problem is the obvious negative to such a device; needing to lose a limb first. Ow. Plus, all the really cool stuff involved with Automail is really just alchemy.
The Punisher very nearly made it because it is truly an incredible device. It’s three weapons in one, a rocket launcher, a machine gun and it contains several fully loaded pistols. Plus it acts as a shield and just looks awesome. The major downside is the sheer size and weight of that thing. I really like it, and I’d love to wield it, but that is a major issue.
So, by the powers of deduction, you can surmise that the 3D maneuver gear won out. This is a device that is not only awesome, but it’s compact, fairly lightweight and is a device meant to make travel more convenient while also providing soldiers in the world of Attack on Titan to stand a fighting chance against beings much larger than they are.
For those unfamiliar, maneuver gear is a device placed on the hips of soldiers. Using triggers, they shoot out metal cables with hooks to forcibly latch onto any surface that it can bust through, usually trees, buildings and sometimes even the titans themselves. It’s a web-slinger, to a degree.
The gear also holds the blades that the soldiers use to take down the titans with the triggers for the hooks residing in the hilts of the swords.
The only real drawback to this device is that it runs on fuel which can run out incredibly fast if you don’t moderate it properly. While this is just an inconvenience when training or using them for recreation, this can be a death sentence if titans are around. It’s also obviously useless in open areas. While some may be fairly unimpressed with this choice, it is the option that I would say is the most fun. Falling would suck, but it’d be awesome to just swing around a city or forest like that.
Honorable Mentions: The death note, the borgs from Alien 9.
The Anime Madhouse 
Good choice! Also, what I really like about the 3DMG is that it’s so intricately designed! So much engineering has been put to it. Props to Isayama Hajime for the smarts! It was amusing to read the extra pages in the first several chapters of the manga. 😀
But! I think if the 3DMG were real, they’ll be really difficult to master. Swinging your whole body with just metal cables to support you will prove to be quite painful. Oh the hips would surely hurt. Gotta be a master at balancing first before trying out the 3DMG!
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