Aki-Sora
English name: Aki Sora
Genres: Romance, Erotica
Type: OVA, Episodes: 1
Aired: Dec 18, 2009
Studio: Hoods Entertainment
Source: Manga
Rating: R+ - Mild Nudity
Synopsis:
Sora Aoi has always been close with his siblings. But while Nami may be his twin sister, he and his older sister Aki share a different kind of relationship. 

What began as an encounter with Aki in the bath led to a startling realization for Sora: he is in love with her. But while Sora is hesitant about his forbidden feelings, Aki confesses that she has always loved him. With their affections out in the open, the two begin a secret relationship.