In one house, there’s the Kinomoto family which consists of a mother and her 5 daughters who are always wishing for a brother. Next door is the Yazaki family made up of a father and his 4 sons who have always wanted a girl in the family. The two parents then come up with a great idea and decide to swap one child each for 3 months! The boy chosen to go into the Kinomoto family is the protagonist and the first challenge he faces is getting all the girls to call him “Onii-chan”. The protagonist’s new family life starts now.

(Source: Liemyx's blog)