When most people think of the aiki arts, Aikido is what comes to mind. Unfortunately, the Ueshiba family has made it clear their vision for Aikido does not include fighting or contests of any kind. But the aiki arts as a whole are often subject to ridicule if not complete dismissal among the majority of the martial arts community. We get lumped in with the likes of George Dillman and his no-touch knockouts, which are nothing more than the power of suggestion over highly susceptible individuals.
Real aiki, on the other hand, is a set of biomechanical principles and processes. When you understand what you are looking at, everything is supported by sound principles of physics. The training methods, however, must be felt to understood. The better one is, the more fake it looks. My teacher once said "if you understand what just happened to you, it's not aiki." So again, we have another case of secrecy killing the art. But why?
These exercises are similar to the solo forms practiced in Taijiquan, Baguazhang, Xingyiquan, Qigong and even yoga. To test one's development of the aiki body, one then practices Aiki no Jutsu (techniques of aiki). These are in essence connection drills designed to isolate certain aspects and test one's ability to receive, process and return force along various vectors to cause structural disruption in another person. It is not about what you do to them, but rather how you move your body and because they chose to grab on they come along for the ride. Some examples of Aiki no Jutsu are:
Now, the very first criticism these drills receive is "let's just say they are real. All you have to do is let go." And you're right! But let's look at a couple factors. If we are to assume these are being practiced with martial intent, the person grabbing you is doing so to restrain you. Why would they let go if their goal is to hold you down? Second, when you achieve kuzushi, the body's stabilization instinct kicks in and then they physically can't let go. Imagine you step off a curb without realizing it. Your arms shoot out naturally, looking to grab onto anything stable to regain yourself. This is what's happening here, except the thing stable is the person throwing you. Let's make it more relatable.
The first real context for these drills becomes apparent when you understand the person being grabbed has a blade in their hand. While we often see these as reactive exercises, in truth the person doing the grab is probably trying not to get stabbed. Then of course, you have even more motivation to try to maintain control of the person and not just let go. If the person grabbing does initiate contact, it's often to pin the other person down or seize control of their weapon. So in either case, the validity of these Aiki no Jutsu can be found in weapon retention:
But let's take it a step further. The principles of off-balancing and structure do not change. Therefore, they can be great in standing grappling situations. Lately I've had the opportunity to work with some really high level judoka, including Olympian Lauren Meece, and wrestlers, including Willie Ray Wilson from Pemberton College (featured in the video below).