"People are more likely to respond well to something that looks at least vaguely like them than they are something like the Hunters. As for why Onari instead of one of the other humanoids, it's partly because we were made specifically to deal with you, and thus we were created to bear as close a resemblance as we could, and partly because the Mistformed is one of Akna's daughters, and was therefor more familiar with your form than those created by other deities."