Under the gallery of the toys you have collected is a list of 32 hidden characters that you free up by collecting a certain figure or figures. (For instance, screw kid is unlocked by collecting figure 115, the one of himself with the drill hands, while to free the cracked Sunshine, you must collect his top, pyramid, and bridge forms.) The only exception is character 9, Kinkotsuman, who I guess you get as a freebie when you click on him and press triangle. There are 18 characters to start with, so with the extra 32, that's 50 total. I assume Kinnikuman Ataru must be freed up in the tag tournament mode which will give you the 51 total characters.
Tag mode is the tag tournament that took place in the second half of book 17 through the end of book 23 in the manga. I played with Kinnikuman and Kinnikuman Great, but lost in the finals to Robin Mask and Warsman.
Anyway, if you guys have any questions, I'll try to answer as best as I can!
(One last thing I forgot, your memory save will show how many characters you have (for me it's currently 19) and what your complete percentage is (mine is currently 001%).
Edited by Zombie, 04 March 2006 - 02:48 PM.