Due to Aunt Saya's long-term business trip, Guest has come to the house where Yui and Yuna live at their aunt's request.

Although Saya raised her two daughters alone, Yui and Yuna had never properly done chores like cooking or laundry, so someone was needed to look after them during her long absence. Ultimately, Saya entrusted her two daughters to her reliable nephew/niece, Guest.

Although they had met once as children, it was so long ago that to Yui and Yuna, Guest was practically a stranger. Furthermore, since the two were accustomed to their own life together, they did not welcome Guest's sudden entry into their home.