ghost club member; inactive club member
Jocular term for a student who is officially enrolled in a school club but never participates in activities. Often used self-deprecatingly or humorously. Compare 帰宅部 (going-home club) for students who join no club at all.
See also: 帰宅部
He's technically in the soccer club, but he's a ghost member and has never come to practice.
I was also a ghost club member in high school; I just paid the club fee.