Elle is a king girl and the best friend of Ark, who ever is taking care of him and waking him every morning. Both lives on a underground village called Crysta. Ark and Elle always wanted to see the Outside World.

Elle actually is a copy of the Elle of the Outside World (Real World) and she dies when she protects Ark from Yomi who wants to kill him, Elle kills Yomi, however she dies too, saying her feelings to Ark before her death.

--- Source: Terranigma/Tenchi Souzou Manga http://www.mangareader.net/1368/tenchi-souzou.html And the original game for snes (same story and same creator of the manga)