The Legend Of Heroes: A Tear Of Vermillion Codes -

Bonus characters
Have a cleared saved game file from Eiyuu Densetsu 3: Shiroki Majo on your MemoryStick Duo. Load the file when prompted in the Japanese version to unlock characters from that game. 

Defeating Bosses
Before fighting any Boss, get all of your characters' deadly attack meters full. Then, fight the Boss and use all your deadlies on him until he has been defeated. Then, pick off the minions.