In the Terrible Urd book, Belldandy says:

"We all have the same father.  So we're still half sisters at least."

And you can see in Fujishima's drawings that Urd looks a lot like the
other two, in such details as the nose and chin, but Skuld has even more
features in common with Belldandy.

And Belldandy also says:  "...Mom gave us when we were kids."

So there is no evidence that Skuld remembers her mother at all.

So I gotta real strange theory.

Belldandy's (and Skuld's) mom is alive and well, but the father of the
three goddesses is dead.

Skuld's mom went into seclusion after this unknown god kicked the bucket
and is now pining for the fjords, leaving the goddess sisters under the
care of uncle Kamisama.

The goddesses therefore have the respect for K0 (Kami -> Rei == Zero) that
they show in the manga, and he feels a special duty thowards them that
explains the strange actions he has taken towards them.

And therefore the goddesses never call K0 daddy!

Everything is neatly tied up and we only have to wait for the end of the
current cycle to witness the catfight of the mommies.

	Henry J. Cobb	hcobb@slip.net          http://www.io.com/~hcobb
    Any sufficiently cool technology is indistinguishable from religion.