18+ Fukubiki! Triangle: Futaba wa Atafuta ♥

Futaba Shinonome is in love with her older sister's boyfriend, Ushio Irifune. However, he always rejects her seductive advances. To pressure him into making love with her, she makes him drink a glass of water mixed with an aphrodisiac. Consequently, Ushio's inner sexual desires awaken, much to Futaba's delight. But, things do not go according to her expectations...