From the video, it looks like it would be EXTREMELY difficult to make it open exactly like the game.
Now, if you do want to have it so the blade sort of swings open like that, you will need to make the blade in a couple pieces, and offset the weight at the ends of each part. Hopefully that makes sense.
If you just wanted to have it spring open, that switchblade idea or butterfly knife (I think those are the names) like DarkCloud and Penlowe mentioned look pretty promising.
If you want more help, ask here or PM me, and I'll see what I can do.
So have a few cosplays I want to do, but no idea when/if I will get to them.
In the mean time, I started up my website for my props, cosplay, and useful stuff. Please check it out