My First Love Is Too Embarrassing to Tell Anyone

Chiaki is good-looking, academically excellent, athletic, and born into a rich family with a super beautiful little sister. He leads a smooth sailing life but still has a 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 that he has lost the appearance that he was so proud of, but when he looks at himself in the mirror, he sees a very cute girl in the reflection. He immediately goes to show it off to his twin sister Kaede, who happens to be very popular with the girls, but there is also something very strange happening to her… This is the story of Chiaki, the second daughter of Saitama Prefecture's three beautiful sisters ―― a dignified first love story that is not embarrassing at all.

(Source: Dengenki Bunko, translated)