Unlock the following characters by completing the corresponding tasks:

Frank
Reach level 90 in online mode. To select Frank in campaign mode, hold Triangle at the mission selection screen. In multiplayer mode, he will appear with the other characters.

Luka
Get all target markers in all missions. To select Luka in campaign mode, hold R1 at the mission selection screen. In multiplayer mode, he will appear with the other characters.

Joe
Complete campaign mode. To select Joe in campaign mode, hold Square at the mission selection screen. In multiplayer mode, he will appear with the other characters.

Megaman
Complete 100 fights in online mode. To select Megaman in campaign mode, hold Square + Triangle at the mission selection screen. In multiplayer mode, he will appear with the other characters.