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Thousands of years before Moana, Motunui was the home to the world's first great navigators. With their resources, they explored the open oceans freely and triumphantly. However, due to the actions of the demigod Maui, the world surrounding the island became overrun with darkness. It was eventually declared that the sea was too dangerous for exploration, and the inhabitants of the island's village were thereby forbidden from ever leaving the security of the reef (though the true reason as to why had been kept confidential from the following generations).
Motunui looks like a typical Polynesian island, with a hot tropical climate, white-sand beaches, crystal clear waters, many trees including coconut palms, houses made of wood and straw, and high earth elevations (mountains).
The name of the island can be from Maori origin, coming from the Motunui settlement in northern Taranaki, in the North Island of New Zealand, or from Rapa Nui origin, coming from the Motu Nui islet in the south of Easter Island, Chile.
Although the name of the island is indeed of Polynesian origin (see trivia above), there is no Motunui island in real life. The filmmakers chose to create a fictional island in order to equally represent and honor the Polynesian peoples and their cultures without giving clear preference to just one. This way, Motunui embodies the culture and traits of many Polynesian peoples and their islands.
The people of Motunui might have been inspired by inhabitants of the real-life islands of Samoa, which are frequently referred to as the "Navigator Islands".