Complex sentence: As Feeder began to take off, Taka began to consider quitting, he had only planned for his music to be a sideline and was unwilling to give up his graphic designer's job to do it professionally.
Split into simpler sentences: As Feeder began to take off, Hirose began to consider quitting. He had only planned for his music to be a sideline, and was unwilling to give up his graphic designer's job to do it professionally.