Aki-Sora(2009)

The Aoi siblings, Aki and Sora, are as close as a brother and sister can be. But as Sora enters high school, he realizes that his feelings for his older sister go beyond simple family ties. Oblivious to her sibling's affair, Sora's twin sister Nami attempts to get her best friend to go out with him. And unbeknownst to either of them, Nami harbors a deep and jealous lust of her own. Aki-Sora is a love story, for sure, but whose love will be returned? Whose love goes unrequited? Can the bond between brother and sister be strengthened by romance, or will Aki's and Sora's affection drive them apart?