The Hanabishi and Hidaka families were planning a long-term international business vacation together one day. Kouki eventually moved in with the four sisters. And one of them has made a fiancee pledge to him. Who should he choose, though? Momone, the second born daughter, is the third wife material: she adores Kouki and does nothing but spoil him. The youngest daughter, Anzu, is the fourth wife material: she has difficulty expressing her true thoughts and is more brattish.