Watashi no Hatsukoi wa Hazukashisugite Dare ni mo Ienai

Chiaki is good-looking, academically excellent, athletic, and born into a well-off family with two beautiful sisters. He leads a smooth sailing life, but he still has one problem. He's not popular with girls, and has never once been in love! He vowed to make a fresh start in high school and spend his days being pampered by girls. The morning after making this vow, Chiaki wakes up to find that he himself has turned into a girl. He is shocked to find an unfamiliar face staring back at him in the mirror, but when he looks again, he sees a very cute girl in the reflection. He immediately goes to show off his new look to his twin sister Kaede, who happens to be very popular with the girls, but there is also something very strange happening to her… (Source: Young Animal, translated)