It comes down, and Tidus doesn't wait to see if it's not moving, if it's down for good - he goes in, not needing to use any special talents for the wide jump he makes to throw himself towards it. He does for getting his blade out though, which jerks in his hand as it's drawn out, but not enough that he can't sweep it forward in a slash before the bird might rise again.

Whatever toughens its body, it's not fully impenetrable, and a dark blood oozes across its stiff wings, its chest. Twitching, but Tidus takes a few steps back, taking that to be spasms.