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.

Saya had raised her two daughters alone, but since Yui and Yuna had never properly done housework like cooking or laundry, she needed someone to look after them while she was away for a long time. In the end, Saya entrusted her two daughters to her reliable nephew/niece, Guest.

They had met once when they were young, but it was so long ago that to Yui and Yuna, Guest was practically a stranger. Furthermore, since the two were used to living only with each other, they were not pleased with Guest suddenly entering their home.