Digimon is a Japanese anime television series . It is about digital creatures called Digimon . The third Digimon series , which began airing on April 1 , 2001 , is set largely in a `` real world '' where the Adventure and Adventure 02 series are television shows , and where Digimon game merchandise ( based on actual items ) become key to provide power boosts to real Digimon which appeared in that world .