To fight Akuma instantly without fulfilling any in-game requirements, hold the Start button and select arcade mode in Street Fighter Alpha 1. Select your character and any additional options (such as Turbo) while still holding down start. Immediately after, press and hold Medium Punch and Medium Kick buttons (Triangle and Circle) while still holding down the start button until Akuma appears. You have to be very quick into pressing Medium Punch and Kick after selection. Do not press any shoulder buttons until Akuma appears or you may invalidate the code. If done right, Akuma will do a Shun-Goku-Satsu on your 1st opponent and you get to fight him next.