The No. 1 little sister type idol 'Lucarina' takes on the roles of four slightly different and mischievous sisters! ! The serious and determined eldest daughter, the cold S-type GAL second daughter, the otaku third daughter who speaks Kansai dialect, and the lively short-haired fourth daughter. "Onii-chan, can you promise not to tell anyone?" An incestuous love and sex drama about four overly perverted sisters who approach their shy older brother. A must-see for sisters who are crazy about moe! ! !