Mixed up with another family's child as a baby, high school student Nagi Umino is finally meeting his biological parents.

On the day of their meeting, he happens to encounter Erika Amano, a high school student at a prestigious and wealthy girls school. At her request, he's half-forced into pretending to be her boyfriend so she can avoid marrying her fiancé...

However, not only were they the babies who had been mixed up, they're also engaged to each other!

The loving parents of both families officially recognize their engagement, and the couple begins living together.

Nagi is in love with his classmate Hiro Segawa, and Erika is determined to rebel against her father, so the couple agree not to get involved with each other.

The mixed-up and chaotic romantic comedy starts now!

[Source: Crunchyroll; emended]