19-year-old Segawa Yuuta was looking forward to starting his new university life and living the normal university life, making new friends, etc, etc. But suddenly, when the plane his elder sister and brother-in-law were on went missing, he became the "father" of his three young nieces! Now, his six-tatami mat apartment not just has to accommodate himself, but 14-year-old Sora, 10-year-old Miu, and 3-year-old Hina. What will be the fate of Yuuta?