After school, the third-year high school student Mitsuki's daily routine is to play with the neighborhood kids. As he was playing as usual, a scary-looking man with a scar on his face approached him! He said he wanted to know how to interact with small children for his new brother who will be a new family member due to his mother's remarriage. The scary-looking man turns out to be Kyohei, who lives nearby and is one year younger than Mitsuki. As they spend time together, he discovers Kyohei's clumsy kindness, which is contrary to his look..?