 Belldandy and her sisters are based on the Norns, who were the  goddesses of fate in Norse mythology. Belldandy (Verthandi) was the  goddess of the present. Urd (Urthr, Urdr) controlled the past, and  Skuld represented the future. They lived at the base of Yggdrasil,  the World Tree. In the original "Aa! Megamisama!" manga, the  computer system used by the goddesses is also named Yggdrasil.