Nautilus is the advanced submarine vessel featured in Fushigi no Umi no Nadia. It serves as a major setting and key vehicle for the series, carrying Captain Nemo and the crew of the Neo-Atlantis resistance. The Nautilus is central to many of the story’s battles, escapes, and underwater exploration scenes. Although not a person, it functions almost like a character itself, symbolizing mystery, technology, and defiance against Neo-Atlantis.