Every 1000 years on Tamagotchi Planet, a special planet change occurs called Tamagottsun. This is when two Tamagotchi towns, Dream Town and Tamagotchi Town collide to make one new town called Dreamtamatown. The story focuses on this occurrence and the interaction of old and new Tamagotchi characters from both Dream Town and Tamagotchi Town anime series. Source: tamagotchi.wikia