(Short for: OniAi) Himenokouji twins Akito and Akiko have finally reunited with each other after separation due to the death of their parents. After six years of living apart they suddenly began to live under the same roof due to Akito's desire to live as a family unit once more. Things were fine at first until Akiko began to express her incestuous love for her older brother, who only sees her as a little sister.