[Calico]

Lyricist: writes lyrics
Composer: Arranges notes for lyrics (like how it's sung)
Arranger: Chooses instruments and their place

Ayu writes her own lyrics, but she doesn't always compose...that's when she's CREA. As CREA she controls the notes of the song, her first being M. In that case she was the one who controlled the beat and pitch of the song. Sometimes she collaborates, like with HAL or DAI.

I hope that made sense. =\

Edit: The way I would see it, lyrics are almost always written first. You can still count syllables that way for when the composer comes in. When I write a song, I usually do it that way. But I could be wrong on Ayu's part. *shrug*