Re: Regrading grabs in Aikido...
The unpronouncable one is right. The first grab is to try and prevent you drawing the sword, or to stop you trying to cut with it if it's already out. Moving behind is a safe direction to go, and also an easy follow up attack.
Josh is also right, the techniques we train in Aikido are aimed at teaching principles, from a simple to understand perspective. Once you have an understanding, they can be applied to any attack.
Edwin's right too. Once you understand the principles it's all about your movement, techniques become a result of your movement rather than a result of your thought process, i.e. you don't think he's grabbed me I better do nikkyo, you just move and let whatever happen happen.
That's not to say everyone else is wrong, just picking out the bits I would have focused on.
In my class we train from the front moving behind, static from behind, and also add attacking from the side, you never know who's gonna step out of a doorway when you're walking down a street or alleyway.