Complex sentence: He served as the head coach of Japan Football League side Omiya Ardija in 1998, then took various other positions at Omiya, including the youth team head-coach and the head of development.
Split into simpler sentences: He served as the head coach of Japan Football League side Omiya Ardija in 1998. Then, he took various positions at Omiya including the youth team head-coach and the head of development.