OVA produced by the manga publisher Toranoana.

A secret intercourse begins when a woman teacher feels lonely because her husband left her, then secretly, the female teacher plays with her teacher's friends at school. And one of the girls who knows the secret relationship wants to also follow-up sex. And at night at school, it all turns into a cosplay haven with 2 women having sex party.

(Source: Translated and Edited from Nekopoi)