A redditor going by KouriKustoms has put together a scale chart based on the characters and weapons in the Kingdom Hearts series of games, including KH1, KH2 and Birth by Sleep. The chart comes with approximate real-world sizes, giving viewers a good glimpse of the size these weapons would be if they actually existed.
Beyond that, there isn't much more to say about these Kingdom Hearts models. Kingdom Hearts 3 isn't even coming out this year, so fans will have to make do with stuff like this to keep their interest in the series piqued.
According to the guy who made the chart, he downloaded the character and weapon models and went about his business. Here’s what he did:
You'll need software capable of viewing 3D models. You might be able to find an obj viewer online, but I'll go over a few programs I've personally toyed with.
I'm currently using Milkshape 3D, because of its simple interface and support for multiple game formats, but mostly since I'd already bought it a few years back. It's old software, though, and tends to crash on some Windows 7 configurations. In High School, I tinkered with Anim8or. It's not a very powerful 3D program, but it should be enough for you to view obj files.
I've heard great things about the free, open-source program called Blender. However, it seems the interface was designed to be efficient, not intuitive, so there's a pretty steep learning curve.
