Haruka and Sora Kasugano are coming home, to a place filled with memories.
Having lost their parents in a tragic car accident, the twins resolve to return to the countryside and start life anew at their grandfather's house, the haunt a constant reminder of moments from their past. Greeting them are childhood friends Nao Yorihime and Akira Amatsume, and newcomer Kazuha Migiwa. It is a warm welcome, symbolic of the days that should come.
Their peace is merely ephemeral, however, as suppressed emotions, born from vows both newfound and forgotten, start exerting their influence on the twins' new lives. And deep down, a dark secret, only known to them, begins to unshackle.
Based on the visual novel by Sphere, Yosuga no Sora not only explores the power of lost memories and true love when the bonds of many become intertwined, but also raises the questions of morality and social acceptance.
Summary taken from: MyAnimeList