Hmm a technique without a condition. I like it, it makes you the bait and you chose shield so that puts you at a considerably good place to defend yourself. However, that's a long winded way of saying your opponents will target you instead of anyone else. Im not criticizing it! No, I just want to make sure I've got what your mean.

Aggressors automatically consider him the highest threat and will target him before assaulting others.

It reads to me that once used the ability draws their attention to you but after their initial attack they may chose to fight others. While this can be useful to me it seems a bit foolish. You're better off intimidating them than just aiming to draw attention.

By that I mean this is a provoking technique which lasts barely any time at all. Since heartless will be your opponents most of the time it can be 50/50 if they actually continue fighting you instead of just going for a weaker foe. 

If you intimidate them, that's another story. You will remain in their mind through the battle. They will fear you and wish you ill.

So what's the difference? Wording. 

I recommend adding intimidate to the effect part.

suggestion: Opponents are intimidated by the tremendous sound, stealing their attention from whatever they are doing. 

In any way you word it, I will have to add a weakness. Your technique may no work on a foe when you are bluffing strength and they have seen through it, due to obvious power differences.

This prevents you from just screaming at high level opponents who outclass you more than reckless heartless. Also, it forces you to improve yourself further, when bluffs get called you're next on the chopping block.