Aki Sora: In a Dream (2010)

The story revolves around Aki and Sora Aoi, a pair of brother and sister who have shared an intimate bond since childhood. Growing up, both have realized the true depth of affection they feel for each other, consummating their love in secret. They are living with Sora's younger sister, Nami. Nami, who has no idea what happens between them try to establish a relationship between Sora and her best friend, Kana Sumiya. Despite these relationships Nami seems to feel something for Sora too, but kept secret.