A hidden weapon it seems, which isn't noticeable when you look at the shoes in the rear view.
I used to think that that high kick is a show of his incredible articulation, but it turns out that he's showing the use the weapon. XD
Also, a larger box art of HGUC Kshatriya (click for larger view):
* MG Blue Frame Second Revise - October 22th release, 5,040 Yen (inclusive of tax).
* HGUC Kshatriya - October 15th release, 4,725 Yen (inclusive of tax).
All images are from Ruli PlaModel Forum.