Go to the indicated coordinates to find the corresponding costume for purchase for Koins.
Press Up(2), Triangle at a character variation selection screen to play as that base character.
Fight through the Premier Living Tower until you reach your sixth opponent. Win that fight with a "Flawless Victory" with either a Fatality or Brutality at the end. You can restart the match if they take a hit and not be disqualified. After the match, you will start the "Secret Battle" against Reptile.
While playing Living Towers you will eventually unlock the Juggle modifier. Use it to lower gravity, which will make juggles easier and allows an easy 10 hit combo when you corner an opponent.