Because their parents weren't home since they were young, they supported each other and were close siblings. Especially the older sister, who had just turned 20, had an abnormal amount of love for her younger brother. She also has a strong libido, and spends her days comforting herself while thinking about her younger brother. Finally, the older sister, who could no longer stand it, puts aphrodisiacs in her younger brother's drink and crosses the line into incestuous fuck! Furthermore, when her younger brother says he has a girlfriend... the older sister, driven mad by jealousy and lust, adds more drugs and falls into a climax sex nymphomaniac intercourse!
