You might wonder why Microsoft decided to publish Mark of the Ninja, an independently-developed 2D stealth game that looks and plays like very few other games out there.

Today Kotaku can reveal the pitch video that Ninja developers Klei Entertainment showed Microsoft in late 2010 to get them to fund the game. You can watch it above. It looks a lot like the final version of Mark of the Ninja, which came out on Xbox 360 last month. Minus the gameplay.

"The genesis of Ninja was quite literally just a video," Ninja designer Nels Anderson told me during a recent phone interview. "There was nothing playable there at all... [but] Microsoft thought that video was so darn sweet, they didn't care, and they signed it."

Mark of the Ninja hits Steam today. Don't sleep on this one, folks. If you're into stealth games—or if you're into games that will get you into stealth games—Mark of the Ninja is a must-play. It's smooth, stylish, and a lot of fun to play. Both Kirk and I can't get enough of it.