On stage 4 in arcade mode, you will get challenged by a secret character. The character that challenges you is determined by how many LDM you land on your opponent before that, you will get at most 2 LDM usage per stage, so to fight Jyazu or Silber, you must land all 6. If you meet the requirement for Jyazu and Silber, the one who challenges you will be random between these 2. This will help you unlock these character faster.

Unlockable	How to Unlock
Adelheid	Fail any of the requirements.
Gai	KO at least 1 character with a LDM
Jyazu	KO at least 6 characters with a DM, use at least 2 LDM in the fights. No teamates may die
Sho Hayate	KO at least 3 characters with a LDM, no teamates may die
Silver	KO at least 6 characters with a DM, use at least 2 LDM in the fights. No teamates may die