The story follows the journey of Kai, a 10-year-old boy who eagerly anticipates becoming a big brother to his little sister, Luna. Kai's excitement and love for his new sibling are evident as he takes on the role of protector and caregiver from the moment Luna arrives. As Luna grows, Kai remains a devoted and supportive big brother, teaching her life skills, being her companion, and offering guidance through various experiences. Despite typical sibling disagreements, Kai's unwavering love and dedication to Luna strengthen their bond over the years. The story highlights the enduring and special relationship between Kai and Luna, emphasizing the profound connection between a big brother and his little sister.