Twin brothers Haruki and Itsuki are often left home alone by their truant parents and have led a rather unremarkable childhood, until a certain Maria suddenly shows up and stands in as their surrogate mother. Although she has no real reason to show any attachment to the twins, she treats them as family. Little do they know that Maria is more than just a "girl-next-door", as she has something a bit more sensual in mind for the two unsuspecting brothers...