Junya Nakatsugawa seems to always start the class with ikkyo. As the "first technique," ikkyo embodies many aikido principles. It's a kind of shoulder rotation that controls uke and pins him to the mat, but the movements involved in executing the technique encompass much of the basic aikido principles. The photo at left shows Ōsensei laying an ikkyo pin on his uke.
Such movements as irimi and tenkan play an important role, as do even more fundamental concepts such as extension and being "centered." Of course, such things are an important part of all aikido techniques, but these ideas are often introduced to a new student when learning ikkyo.
The class expanded on the theme of Kosadori (cross-hand grab) but the first ikkyo sticks in my mind. We also did kokyu nage (Sometimes called Mae otoshi), which is a projection throw channeling one's power through the upper arm or shoulder into the back of uke's elbow.
Junya's Aikido is very strong and neat. I always learn a lot in his classes. Here's a video of him doing... ikkyo, of course: