It's pretty unfortunate that Shinji had already turned his back to Kai when that grab for the soap went terribly, terribly wrong. Would Shinji even have been able to prevent this tragic fate? This awful slip-up?

He figures out that something is Amiss pretty quickly, but it's not split-second enough for him to even attempt to catch Kai as he takes that fall. He only manages to catch the sight of the collision, his whole body tensing up in shock.

Oh. No.

"Kai?!"