its name should be from mythology, but the name should not be one associated with creation or underworld themes
Hmmm... the list seems pretty short on beings from Russian/Slavic mythology. My first thought was Кикимора (kee-KEE-more-ah), which is not the proper name of a particular mythic figure, but is VERY roughly translatable as "female house-elf" in the Harry Potter sense.

I like it because (a) it sounds pretty, and (b) as a house-sprite, a kikimora lived in close proximity to humans, and the asteroid (101955) 1999 RQ36 is comparatively near to our own "house," the Earth. (Moreover, although a kikimora is sometimes helpful and protective of the household, when she's in a bad mood she may cause harm -- and there's a small possibility of this asteroid impacting the Earth at some time in the future!)

As far as named deities of Russian paganism, Перун (peh-ROON) is an obvious choice because he's a lightning/thunder god and thus associated with the heavens. On the other hand, he's such a major figure in the pantheon that, possibly, there might be some myths identifying him as a "creation deity," which would disqualify him.

But here's an English-language list of Slavic deities that you might want to consider, rockzmom. Obviously, some might be disqualified because they're too connected with the underworld (like Veles), and others might already be in use for other asteroids.

P.S. Whoops, cancel that "Perun" suggestion... I just checked, and apparently there's already an asteroid (not in the near-Earth-object category) named after him.