Youko (ようこ) is a former member of BiS. She was a fan who won an internet auction to become a member for one day only. She was initiated into the group on June 6th 2013 and left the same day. Not much is known about her.
- She has the shortest tenure out of every former BiS member.
- She was an idol for the same amount of time that SiS existed as a group.