What can I say - it satisfies my inner sadist.
Nikkyo can/does/should hurt like a bolt of lightning going up your arm when applied properly. It will bring even the biggest guys to their knees in an instant. It's the one technique I use to show what Aikido is in 30 seconds, or less. The pain itself is produced from compression of the medial and radial nerves in the carpal region of the wrist. Best of all, it can be released just as easily as it was applied with no real lasting damage to uke. It's a great self-defense technique and has many "real world" applications as well. The version in the vid is a bit "stiff"/formal, but that seems to be a common approach in many Yoshinkan schools. Here' another approach. Jump to the 3:40 mark for Nikkyo demo.