The haori can be done with pretty much any costume pattern that has a sleeveless robe. I've seen one for Harry Potter wizards that would work, some Easter Passion play costumes that would be even simpler, so on and so forth. I make mine from scratch with basic shapes but I think of all the patterns I have in my stash, the Harry Potter wizards (I forget if it's a Simplicity or McCall's pattern) is probably the closest - the right sleeve openings, enough flare in the bottom, etc. Just remember that it's lined with a certain color (I think Hitsugaya's is forest green) and has a split up the back from the hem to about mid-thigh.
The pants are hakama. Use the Folkwear hakama pattern, it's the easiest for beginners to follow - though it's not a beginner project by far. Most of the tutorials online are a lot more difficult to follow unless you know a lot of historical costuming techniques. Do a google search for Folkwear patterns and you'll find it lots of places online.
Founder and President, Madison Area Costuming Society, a chapter of the International Costumer's Guild
Strange Land Costuming - www.strangelandcostumes.com