A modern teenager accidentally transmigrates into a book, turning into the young imperial prince Xiao Zhichen, and becomes the biological younger brother of the cold and obsessive Eldest Princess, Xiao Linyue. Knowing in advance the tragic fate of his sister being cold and paranoid and ultimately self-immolating, he resolves to protect her with an infant's warmth. Using his heartwarming companionship, he slowly melts his sister's defenses, step by step reverses the plot's trajectory, resolves grievances and entanglements, and rewrites the originally scheduled tragic ending. Relying on each other and guarding one another reciprocally, the brother and sister harvest warmth and fulfillment deep within the imperial palace.