Kakurenbo: Hide & Seek (カクレンボ, Kakurenbo?, lit. "Hide and Seek") is a Japanese cel-shaded anime short film written and directed by Shuuhei Morita.

The film is based around "Otokoyo", a game of hide and seek played by children near the ruins of an abandoned old city. The children who play this disappear, believed to be spirited away by demons. Kakurenbo follows Hikora, a boy who joins the game with hopes of finding his missing sister. The story line is built on the idea that Tokyo is losing its natural aesthetic, which includes child's games such as hide and seek in order for industrial progress to ensue i.e. lighting the city of Tokyo costing innocence of childhood games.

Source: Wikipedia