The older brother of the Onami family lives with four sisters, Sora, Akane, Kohaku, and Sumi. Having been suffering from severe asthma when I was little, my daily routine is to "sleep with one of my sisters". One day, my parents, who were also researchers, ordered me to carry out a demonstration experiment of "improvement of immunity by hugging". It says, "Hug your sister with love for at least 10 seconds before going to bed every day." And if some conditions are not met, there is no effect. Aside from the embarrassed older brother, the younger sisters decorate the condition with a frame in the living room as the five rules of the hug.