Oni Island

In addition to including Momotaro as a cameo, Katamari Damacy also features the dangerous and enigmatic Oni Island ("oni" means demon in Japanese), to which Momotaro travels in order to defeat a band of marauding monsters. Juliet Piggott writes, "The people of the area were being terrorised by a number of oni which inhabited an island and were making raids on the mainland to steal its treasures" (89). In the game, this demonic land appears as a small island far in the ocean which players can roll up once their Katamari ball has become large enough.

(Katamari Damacy, np)

Katamari Damacy makes reference to the negative nature of Oni Island by classifying it as "evil," as evidenced by the screenshot above. Likewise, the game hints at the famous tale of Momotaro by describing the island as a place where monsters live and treasure lies. Unfortunately, players aren't able to actually explore the island, so they'll have to take the game's (and the myth's) word for it.