Oreshura

The protagonist, Eita Kidou, is a high school freshman with excellent grades and a disdain for love. He used to live a regular school life with his childhood friend, Chiwa Harusaki, a girl who's nearly a sister to him, but then one day the school's most beautiful girl, Masuzu Natsukawa, confesses to him. However, her true desire is only to fool the eyes of others and pretend to be a couple. With a certain secret of his in Masuzu's hands, Eita is forced to play along… But a fierce battle over Eita begins as his ex-girlfriend, Himeka, and his fiancé, Ai, join the fray!!"