Kurumi is a shy and innocent beautiful girl, still immature in both mind and body, who devotes herself to her older brother with pure, untainted affection. Smiling brightly, she invites him to play, and when he embraces her, she softly murmurs, "My heart's racing... it's so warm." This tender story gently takes the hand of such an adorable little sister and guides her into the adult world. Filled with heartfelt moments that convey her innocence and genuine emotions, this is a deeply moving experience.