I have one video I can reference:
Specifically the very beginning, but the principle he's demonstrating throughout is ok, though a bit too floppish. At least he's not doing the electricity type demo that is often seen.
Anyway, the beginning is to me, great. He's connecting to uke's center, getting under them and lifting his arms (and uke) without using his shoulders/chest/biceps, very smooth and relaxed and uke is actually putting some weight into him. It takes a very specific type of body training to be able to do that.
Have someone hold a jo arms lenght out from them, horizontal. you stand facinng them and also grab the jo at arms length and try to raise the jo up with them putting just a little bit of weight into the jo and see if you can do it using nothing but your arms, but without using yoru shoulders/chest/arms. To call it hard is a gross understatement.
now stand closer to the jo so that your hips are almost directly under the jo and this time whole holding the jo in place, drop your hips down a foot or so (keep your hands on the jo and at the same level they were before dropping your hips) and kind of get under the jo. Now keep the distance between your hand and hips consistent and just stand up. While you will probably still have tension in your shoulders/chest/etc to support the jo, you should see that it's much easier to lift the jo without introducing a whole lot more tension into your body.
In that video, that's what Horikawa is doing, but without physically moving his center to get under uke and without using the normal muscles one would use to do what he's doing. The rest of the demos on the vid are pretty much an extension of that, connecting to uke's center, getting under them and moving them where their balance isn't. That's also pretty much every aikido technique you'll see as done by o'sensei, regardless of era.