leave it on Fast automatic, but attempt to use Shiki in fights. you can even "assist" automatic mode by letting it press the first few buttons, then filling in the rest on your own. Focus on passing the green light back and forth so you only attack with one character at a time...while using Shiki, scribble the bottom screen to keep Neku moving.
you'll get it eventually. It's very worth it to learn using both too, since it makes the game 1000x more fun, especially as you get block and jump skills with Shiki. little by little you'll feel a bit better. wake up, time for us to realize! wake up--FUCKING MUSIC.