Ah! My Goddess [TV] (DVD) 6 Last Dance Description:

Belldandy and Keiichi are caught up in the battle over the Earth's Fate When The Lord of Terror suddenly takes over Urd! The Lord of Terror summons the Demon gate, and woe to us all if she opens it! The world will be overrun by demons. The Valkyrie, Lind, is sent from heaven to execute The Lord of Terror by any means necessary and whatever host body it happens to be using. Belldandy in turn is given the holy flute to summon the mighty Midguard Serpent to fight, but The Lord of Terror can jump from one body into another, therefore escaping peril. Will she be able to take up arms against her sister Urd, or Skuld, or even Keiichi?

About the Ah My Goddess TV DVD series: While staying alone in his dormitory, college student Keiichi Morisato was trying to call some restaurants for delivery when he accidentally called the Goddess Help Line. Suddenly, the mirror near him glowed and a beautiful goddess named Belldandy appeared out of it. She granted Keiichi his one wish for her to be his girlfriend forever. After being kicked out of the dorm, Keiichi and Belldandy now live in an old temple with her sisters Urd and Skuld.