Yuki has three forms of which can be changed by pressing enter. in her first form [the form you start the fight with] press "W" to enter blood heat mode [like that of melty blood] and press "S" to counter the opponent when he/she is attacking. Instead of a regular counter, it will act as yukis final arc [again, like melty blood] and u will see ryoko asakura stab the opponent to death. hope this he