Kobametal (Key Kobayashi) from Amuse, Inc. is the producer for the band Babymetal. What does his team do for the music? Help with musical compositions? Give advice? Give them ideas? What is his role with the band?
It's clear that Kobametal owns this band. It was his enjoyment of both Idol-Pop and Metal that caused him to have the idea to join the genre's. He has full control of the band, he personally hand-picked the girls based on several criteria necessary to perform the music and maintain their status. He determines where they tour and all those key decisions.
I don't fully understand his involvement in the music aspect, as some interviews I've read seem to indicate that he helps write the music but those interviews have been in Japanese and translated, so it's possible some of the meaning was altered in the translation.