Kakurenbo: Hide & Seek (2004) Anime Watch

Among the high rises of steel pipes, meshed power lines, and faded neon lights, exists a game that children dare to play within the ruins of the old city.

"Otokoyo," a secret game of hide-and-seek, one where all who play wear fox masks and only begins when seven have gathered. But it is no normal game, as all who have played it have gone missing. Many whisper it is the work of demons, but that is just a rumor... or is it?

Kakurenbo follows the story of seven children as they play Otokoyo for the first time and discover why if you play, you never return.