One day, Yun-Hyeok suddenly finds himself with a younger brother—Yun-Jae, a sickly child diagnosed with an incurable disease. Determined to protect him, Yun-Hyeok takes on the role of Yun-Jae’s guardian, raising him with unwavering devotion for the next 15 years. But as Yun-Jae grows older, he begins to push the boundaries of their sibling...