College freshman Yuta Segawa is asked to look after his older sister's three daughters — teenage Sora, grade-schooler Miu, and toddler Hina — for a short stay. When their parents vanish in a plane accident and the wider family balks at keeping the sisters together, Yuta takes all three into his cramped one-room apartment rather than see them split up. He juggles classes, part-time work, and a sudden household of three girls while trying to hold the makeshift family together.