The Onami girls' endlessly affectionate brother developed asthma at a young age, which left him bedridden for much of his early life. Now that his health has improved, he does his best to make up for lost time through online learning. His medical researcher parents have used the unique opportunity his illness provides to gather data about his condition, which has greatly contributed to medical science. As a result, they've encouraged him to get plenty of sleep and lead a calm, relaxing life so that he'll make for a better research subject and help people all over the world. However, those same parents throw a wrench into his peaceful life when they come up with an idea to boost immunity through hugging. Now every evening he has to choose one of his sisters to hug! What will Onii-chan do when faced with this sudden and weighty responsibility?