Yuuta Segawa has just started his freshman year of university. One day, his sister Yuri, who raised him after their parents died, asks him to take care of her daughters Hina, Sora and Miu while she and her husband go overseas on a business trip. Yuuta grudgingly accepts, but tragedy strikes when their plane goes missing and all passengers are presumed dead. In an effort to prevent the three girls from being split up,...