One day, Yunhyeok suddenly finds himself with a younger brother—Yunjae, a sickly child diagnosed with an incurable disease. Determined to protect him, Yunhyeok takes on the role of Yunjae’s guardian, raising him with unwavering devotion for the next 15 years. But as Yunjae grows older, he begins to push the boundaries of their sibling relationship. Then one day, through the security cameras Yunhyeok installed to keep an eye on Yunjae, he witnesses something he was never meant to see…