Very base has reverse taper. Suggesstion is to wrap tightly down into soil(just reverse section)with wire and leave in tree. Will expand and make more interesting. Make coils slightly farther apart as present wrap too close together
. Ideas for adding movement NOW good advise.
I would not recommend using this technique. The change where the reverse taper occurs is the graft union. This is a young tree, likely no more than 2 or 3 years from bring grafted. The union is brittle. Attempting to apply wire at that point runs the risk of cracking, breaking or separating the graft union. Graft unions will superficially heal the first year, but they often will not be completely fused for upwards of 10 years. Do not try this wire technique, as you will have a high probability of killing your tree.
If it were mine, after the graft was more than 5 years old, I would simply use a deep enough pot that I could bury the graft union about 1 to cm below the surface of the potting media. Since you are going for a cascade, the deeper pot will not be an issue.
Cork bark Japanese black pines are much less vigorous than the normal form of JBP. Do not be too aggressive with applying techniques. I only de-candle my cork barks once every 3 years on the average. Keep more needles than you would on a normal JBP.