Yami is to op (or Akira is weak it's a matter of perspective). But I agree to you, the idea was to make certain waves of enemies more widespread to be more difficult to Yami and easier to Akira, but in the end I didn't implement it.
Sorry for the lack of options, I had to crunch a little bit at the end and I focused on other elements of the game. T_T
Thanks for playing! I'm really glad you liked it.