Nobody Knows tells the story of four children: Akira, Kyōko, Shigeru, and Yuki, who are aged between five and twelve years old. They are half-siblings, with each of them having different fathers. Because the three youngest children are in the apartment illegally without the landlord's knowledge or permission, they cannot go outside or be seen in the apartment, and they do not attend school. Their mother leaves them alone for weeks, and finally does not return. Forced over time to survive on their own, they can only rely on each other to face the multiple challenges in front of them.
