Futabu!

Niimura Akane is a well-liked girl who has been taken to join the Futa Club as someone who is responsible for "service duty". However, she must pass the entrance test first. Some members are a little bigger than she initially anticipated, but there are some people who are anxious that she is more of a challenge. So began daily events with four futanari in the club. (Source: Translated and Edited from Nekopoi)