Plasma Sword Cheat Codes for Dreamcast

Be Kaede:
First highlight Rain on the character select screen then press Down, Down, Left, Left, Up.

Be Rai-On:
First highlight Byakko on the character select screen then press Up, Down, Left, Left, Right, Left, Up.

Be Evil Gamof:
First highlight Gamof on the character select screen then press and hold Start + A.

Automatically Selectable Kaede:
Though I'm not sure what triggers her appearance, if Kaede shows up in one of the random matches (that is, not five, eight or 'nine') and you defeat her, she automatically appears on the roster of selectable characters from then on. So be sure to save the game!

Fun with Gore:
Select Gore as a character and configure the controller layout to have your taunt on. You can make Gore's head grow by pressing the corresponding button. Roll the D-pad back and forth while pressing the Taunt and he will shrink down and remain that size until the move is repeated.