Halfway through the game you must play a one-on-one battle with your lead character's "rival". You only get one chance, and if you fail, you will not unlock anything. Assuming you beat this character you will continue fighting opponents until you face the last Boss, either "Wild Iori" or "Evil Ryu" (depending on which character(s) you played as). After defeating this character, you are presented with a square consisting of nine smaller squares (resembling the side of a Rubik's Cube). A number of these from 1 to 6 will disappear depending on the difficulty level you have chosen. These squares vanish randomly, and only when all nine are uncovered will the hidden character be revealed. This is tricky because the squares disappear in a random order, and sometimes only squares you have already broken will vanish. Theoretically you can unlock them in three tries, but it normally takes six to nine times for each hidden character, assuming you unlock only one new square each time. These odds are helped by choosing disparate characters. For example, defeat the game fifteen times using Ryu, Ken and Morrigan (similar type characters) without unlocking Akuma, the first hidden character. Then, after using Zangief, a completely different character, Akuma became unlocked. The other characters that can be unlocked are Yuri, Akari, B.B. Hood, Geese, M. Bison, Orochi Iori, and Evil Ryu.