Sakamoto Riku lives more or less a secluded life working as an ero manga artist, until one day, his younger sister Sora arrives at his home, telling him that their father has disappeared somewhere leaving only a goodbye note. Their mother is long gone, so being the only relative that can take responsibility for her, Riku decides to take care of Sora and provide her with shelter and a shoulder to rely on. (Source: MU, edited)