So, today, though worship of the Old Slavic pantheon has long since died out (although there are neopagan revivals), Slavic mythology is some of the most well-preserved and well-known mythologies in human history, with only a few others (namely Greek, Roman, and Egyptian mythology) being remembered better.
Memory of Norse mythology, however, has faded much, like that of many of the other polytheistic religions people followed before converting to Christianity. However, I find it very interesting as well.
Thus, this AHC challenges you to create a world where the fate of the Slavic and Norse gods is switched, with the Norse being very, very well-preserved and prominent in popular culture while the Slavic pantheon are left on the back burner and mostly forgotten by popular culture.