Re: [Water Training Continuation] Kiritsugu teaches Karin
I'm a sensei. '
Okay, you went on a sort of little rant there, haha, I had to reread it a few times. Actually, no the shark would not be slower, it would actually have more power and drop faster.
Naturally, the formula for this is f=mA, where force is mass x acceleration. The bigger the mass, the bigger the impact is. Likewise, because this jutsu is formed on top of the head, (as you stated you made it 21 feet large), I'm quite sure his head is quite crushed if it makes contact with him.
This can also affect your enemy's counterattack - if it's really big, he could have a tougher time escaping this move properly, but if it's too small, he can easily block it. When details aren't stated, people simply assume, and often times, leads to arguments, etc.