The world's deadliest assassin just got the hardest assignment of his life: babysitting. After years of bloodshed, legendary hitman William has finally retired. But his peaceful life comes to an end when an old friend entrusts him with his only child, Ko. At first, the job seems simple. Ko is an energetic 8-year-old with a bucket list inspired by her favorite movies and TV shows. From eating her first burger to seeing the world for the very first time, she's determined to make the most of her life. But when Ko's father suddenly disappears, assassins, criminal organizations, and even world governments begin hunting her. As the attacks grow more relentless, William realizes the girl he's protecting may be the most valuable target on Earth. Now, a retired assassin and a stubborn young girl must race across the country in search of her missing father while staying one step ahead of the powerful forces closing in on them. But why is the entire world hunting Ko?