Play as Katze:
To play as Katze, you need to defeat all 100 opponents in Slash Mode without continuing a single time.
Hold L1 + L2 + R1 + R2 + START + SELECT on the first controller. Doing this will get you out of POV Mode, Slash Mode, Story Mode, and VS
Go into Story Mode. On the P2 controller hold the "Restart Game" buttons. Make sure P1 chooses the right character and weapon the first time around, since P1 won't get to choose twice. Re-enter VS. Mode. P2 will choose character and weapon. Doing this will change the season in VS. Mode.