Aneki... My Sweet Elder Sister The Animation
English name: Aneki... My Sweet Elder Sister: The Animation
Genres: Hentai
Type: OVA, Episodes: 4
Aired: Sep 28, 2007 to Jul 29, 2011
Studio: T-Rex, Office Takeout
Source: Manga
Rating: Rx - Hentai
Synopsis:
Takumi just cannot stop fantasizing about Saki-senpai, her voluptuous body just stands out anywhere. One day she talks to him on the train and they become friends. Whenever he can, Takumi stares at her form, always getting a hard-on. The next day he finds out they have the same fetish... and so the story begins.

(Source: AniDB)