The Earth is the planet where the Prince and the other cousins roll up objects to restore the Cosmos. Inside Earth are full of weird objects, and the place is mostly crowded with objects in the streets, in the water, and in the floor. The King, in the first game, mostly visits the countries of the following: Thailand, Philippines, Portugal, Spain, the Netherlands, Russia, Mongolia, and many others. However, when the Prince rolls in Earth, most of the objects there are Japanese-related. Most of the buildings there are mostly taken from sea creatures. One of the side characters, the Hoshino Family, is located in Earth; they are most likely live in an apartment.
When the King destroys completely all of the stars and the Moon, he commands the Prince to roll inside Earth to restore the stars and the Moon. Before entering a stage, the King states that he goes to countries from all of over the world. In the ending of the game, the Prince can roll up all of the countries.
Again, the setting takes place on Earth. Actually, famous landmarks appear in the last stage.
Earth does not seem to be the setting of Me & My Katamari. As the last stage is called 'Sunflower Continent'. In addition, there is no such thing as 'Sunflower Continent' on Earth.
The setting is on Earth again. Like We Love Katamari, the famous landmarks return in the game. In Schloss Kosmos, you appear in the Pacific Ocean. There, the player can see Asia, Europe, Africa, Australia, Antarctica, North America, and South America. The player can roll up all of the countries and some several cities such as United States of America, Russia, China, and etc. Once entering Space, the player can roll up the Earth.