The skulls will only show themselves if you start from the mission start. Choosing checkpoints will cause the skull to hide or dissapear this is proven

So far from all the armor I have viewed, I think that there are some awesome armor beside the hayabusa armor. For instant I kinda like the scout armor Maybe once you use that armor, your sniper skillz would improve. Btw, I believe lots of people wants the hayabusa armor because it looks cool and who could resist being a ninja in the battlefield. Personally I just feel that hayabusa is nth special but I do love that little katana that he carries around its back.