The Hanabishi family and Hidaka family are next door neighbors. The fathers of both households could be called best friends, so they all get along like one big happy family. In particular, Hidaka family’s only son Kouki was raised lovingly by the four Hanabishi sisters like he was their own brother.

One day, the Hanabishi and Hidaka parents were preparing for a long term overseas business trip together. Kouki ended up living together with the four sisters. And one of them is promised to him as a fiance. But who should he choose?