So I found out who the secret characters are. They are in teams like the main characters, except for the last character, who has no story mode (and probably isn't playable in the 1P mode). The big surprise is that you get to play as spoiler (click to show/hide)
Richter and Maria
. I read that spoiler (click to show/hide)
Richter
is a boss in the game, too. :o
I thought I was done with the game, until I beat a certain boss fight the "right way" and found FIVE MORE portraits to go through! :o Also I can now fight against spoiler (click to show/hide)
RICHTER BELMONT one on one; my level is too damn low right now as he wins if he hits me like twice. You don't die against him, but you do lose items of you use them.
Also it plays the BGM from the first stage of Rondo of Blood. :D