As a former Shotokan Karate practitioner myself, I am quite familiar with the Heian Kata series. However I have never heard of Heian Hyakudan before.
First and foremost, is this a real technique or kata? I've been trying to find out more about Heian Hyakudan through google searches, but I get absolutely nothing.
If we dissect his finishing stance, we might be able to come closer to a conclusion. His bottom section, leg and hip formation is a posture held after jumping or leaping. We also know he is landing from a jump due to his forward shoulder being lower than the back shoulder (as well as the visual landing effect).
The part that throws me off the most is his upper posture. Normally when a jumping technique is executed, both arms work together and are connected(katas: Heian Godan and Bassai Dai). In this picture, his left arm is back which would mean that his technique requires a certain hip motion. The only times I recall seeing the top posture is in a Kata like Chinte, but even then, the leg stance requires feet to be spread out with open or reverse hips.
The top just doesn't match with the bottom. I have never seen a technique like this, nor heard of it.
Please help me identify this specific technique or Heian Hyakudan.