Six years ago, you set out on a journey leaving your half-little sister alone so she can be more independent. Her name is Rio. Today is the day Rio’s beloved onichan returned from his long journey. Six years has passed, little Rio now have grown into a finewoman. However she’s still a clumsy half little sister as ever. When you get home, you find her in the kitchen wearing nothing but apron, you teased her a bit but she took your jokes seriously, when she said she wanted to be your bride she really means it, leading you and her into an exciting atmosphere, and eventually having fun to please each other.