Eudial (Eugeal in the English dub) is the first and possibly the leader of the Witches 5. She first attacks the Sailor Senshi in episode 103. Her name comes from the mineral eudialyte.

In the anime, Eudial seems to be the oldest of the group, and is much resented by the others—particularly Mimete—because Professor Tomoe seems to favor her. A brilliant inventor, she is able to construct and jury rig weaponry and computer technology through the use of everyday items; for example, her Fire Buster weapon is constructed of a blender and a vacuum cleaner hose. Her machine affinity also allows her to modify her computer to track down potential Talisman holders, stealing their pure hearts with a specialized gun and using Daimon to finish the work. She is referred to as Chief by the other members. Eudial is generally fairly even-tempered and level-headed, except as a driver. In many episodes she nearly runs people over, partly because the car emerges from its underground tunnels in illogical locations. She carries a deadly shoulder-mounted flamethrower, the Fire Buster (later upgraded to the Fire Buster II), and later in the series booby-traps the under-construction Marine Cathedral. She actually succeeds in getting two of the Talismans, but loses them to Sailor Pluto. Furious, she escapes in her car, only to find that Mimete has torn out its brakes and filled it with snails. (In the dubbed anime, they are "acid snails" and have dissolved the brakes, although one is shown sitting on her exposed skin without effect.) The car crashes over the highway into the sea below, killing her instantly.

In the manga, she goes by the alias Yuko Arimura and leads Good Etiquette in the Philosophy division of Infinity Academy. Her rank is Level 78. She leads some students to "Mount M" for a retreat and tries to remove their Hostes during orientation. Sailor Mars and Sailor Jupiter appeared and fought her. Sailor Mars used her 'Mars Snake Fire' attack on Eudial but it turned her into a monster looking similar to a Gorgon with a black star on its forehead. She was then killed by Sailor Moon. Although never used in the manga, her strongest attack (according to the Materials Collection) is called "Fire Buster."