Yuri no Hana Tankyuu Club ~Kindan no Triangle~

The "Lily Flower Research Club" in a prestigious all-girls school is actually the front for the lesbian affair of Mei and Mai, the only members of the club.
But one day the two lovers receive a visit (and an application to the club) from Honami, the pure and naive idol of the school, who mistakenly believes their club is the real thing.
Initially, and after some hesitation, both girls decide to (ab)use Honami for their personal (sexual) amusement, but things grow different and out of control in no time...