B
Unlocking Sakura: Play with Ryu, any level, and finish the game.
Unlocking Dan: Play with Sakura, any level, and finish the game.
Unlocking Rose: Play with M.Bison, any level, and finish the game.
Unlocking Fei Long: Play with Abel, any level, and finish the game.
Unlocking Gen: Play with Chun Li, any level, and finish the game.
Unlocking Cammy: Play with C. Viper, any level, and finish the game.
Unlocking Akuma: After unlocking Sakura, Dan, Rose, Fei Long, Gen and Cammy, finish the game in any level with any character you have already beaten the game, no continues, and a required amount of perfects(shown below). After beating Seth, you will fight Akuma. He must be beaten without using continues.
Unlocking Gouken: After unlocking Akuma as shown above, beat the game using Akuma, then finish the game in any level with any character you have already beaten the game, no continues, no round loss, and a required number of perfects, super/ultra finishes and first attacks. After beating Seth, you will fight Gouken. He must be beaten without using continues.
Unlocking Seth: Finish the game with all characters, including Akuma and Gouken.
Notes:
Some of these conditions aren't necessary to face Akuma or Gouken after Seth, but if you don't match them, you will not unlock them for use.
The required number of perfects, super/ultra finishes and first attacks change according to how many rounds are needed to win a match.
For 1 round matches:
1 perfect
3 super/ultra finishes
5 first attacks
For 2 round matches:
2 perfect
5 super/ultra finishes
10 first attacks
For 3 round matches:
3 perfect
7 super/ultra finishes
15 first attacks
For 4 round matches:
4 perfect
9 super/ultra finishes
20 first attacks