Growing Up TogetherEdit
Urd is the eldest of the sister goddesses, and was sent to Heaven by her mother Hild when she was at a very young age. When Urd came to Heaven, Belldandy is already there. Urd is then assumed to have taken a guardian-type role over her younger sister from then on. Many years later, Skuld was born. Since Urd was most likely struggling with her demon side at that point (such as her angel and licensing examination), Belldandy was the guardian over Skuld.
Although they are not full sisters (Belldandy and Skuld are, but Urd has a god as a father and a demon mother) by birth, they are everything sisters embody, especially when it comes to dangerous situations. A dialog from the Lord of Terror arc shows that tellingly.
Keiichi: "You mean Urd isn't really your sister?"
Belldandy: "Shh! Skuld might hear you!"
Keiichi: "Y'mean Skuld doesn't know?"
Belldandy: "Right. In fact, Urd herself might not know either. Actually we're not completely unrelated. We all have the same father. So we're half-sisters, at least. But we grew up together as if we were true sisters! We've always been sisters in our hearts, and so we always shall be."
Skuld: "Urd will always be my sister, as far as I'm concerned."
— OMG, Chapter 35 (DH)
Belldandy rarely disobeys heavenly orders, the prominent situations are when it comes to Keiichi or as the continuing dialog shows, her sisters. While Urd and Skuld use to quarrel a lot, if the worst comes to the worst, they stand together without deliberation.
Keiichi: "So don't you have to contact ... umm ... 'The Almighty One' ...?"
Belldandy: "Judging from his attitude when he spoke to me I'm afraid he won't treat Urd very kindly."
Skuld: "So you intend to disobey orders all by yourself?"
Skuld: "So I'm with you on this one, sis."
— OMG, Chapter 35 (DH)
In fact, their quarrels are much more like an exciting game than something negative. The two chapter mini-story at the end of volume 20 empasizes that, when the two sisters fight for the right to select the TV channel.
Skuld: "Where's the fun in just watching?"
Urd and Skuld: "It's fun because we win to watch."
Keiichi: "Geez, I can't tell whether those two get along well or not."
Belldandy: "Oh, didn't you know?"
Belldandy: "They get along very well."
[Note: Some translations have this line like "I have never seen sisters before who get along better with each other." Probably the first version comes nearer to the original, but don't know really.]
Keiichi: "Is that so?"
Belldandy: <So much so that I feel jealous...>
— OMG, Chapter 129 (EC)
Similarities and DifferencesEdit
All of the goddesses have a core, and that core is very similar when lined up with the sisters. It is a core of kindness, sincerity, and compassion. Belldandy manages to keep this core throughout her life being open. Skuld gradually grows up, and mellows out to become kind and compassionate as well. The first time Urd notices Skuld's maturity is in the Welsper arc, when she says that Skuld is growing up to be more and more like Belldandy.
Urd: "Beseiged on all sides, huh..."
Skuld: "Let's keep going for now. We'll find a way to dissolve it."
Urd: <You're getting pretty similar... to Belldandy.>
Caption: Or not...
Skuld: <Ufufu... if this goes well, then Urd won't be able to hold her head up to me for awhile...>
— OMG, Chapter 97 (EC)
Urd's goddess core is illustrated very literally when Urd's devil side is released; her goddess half is very Belldandy-like.
Skuld and Urd are also similar in the fact that they tend to be motivated by the end of a situation, but get so lost in the means that they toss out the end. For instance, Urd's original goal was to get Belldandy and Keiichi closer together, but it comes off as Urd simply trying to get Keiichi into bed with her. Skuld sees Keiichi's motorcycle and attempts to ruin it, but gets so caught up in the mechanics that she instead tries to improve it.
One more thing they all share is their jealous trait; all three sisters display possessive and jealous tendencies at one point or another, some more than others. Their corresponding pages have sections regarding this trait.
One thing they all share (and even with Keiichi) is their competitive nature. Both Belldandy and Keiichi are motivated by new challenges, such as in racing (Belldandy /is/ the broomracing champion in Heaven, after all). Urd and Skuld are also very competitive when it comes to games, gambling for the television.
Although they're identified by Heaven as Norns, the goddesses don't seem affected by their titles very much in their day-to-day lives. The only time their time domains had a drastic effect on them was in the Trials of Morisato arc, when Urd and Skuld seemingly shot into their time domains; Urd was regressing into the past, while Skuld was skyrocketing into the future.
Skuld, being the Norn of the Future, is also a mecha-fetish genius. This is an interesting contrast to Urd, who dabbles in potions. Machines are considered the future, and require a lot of innovativeness. Potions are usually considered archaic. In other words, Urd's more "traditional" while Skuld is more "progressive". Belldandy, being the Norn of the Present, concentrates on what's happening then and there; this could explain how she relates to animals well, who live only in the present.Among Urd's activities, the activities of watching television, sitting alone, and studying are all acts of either reflection of the past or attempting to not think of the past. Urd has the longest past of the three goddesses, and she tends to either think about it a lot or trying to not think about it.