Looks like if you "move" your rival from where first hit of EX Kachousen hitted him/her, with an Hisatsu for instance like in the stream, second hit of the Kachousen doesn't hit because enemy is no longer where it was.. So i guess EX Kachousen only works for combos if it's a corner combo. Also, I guess if rival is not in the corner and dashes or rolls back after EX Kachousen first hit, he/she avoids second hit, since is not combo.