My take on the shape behind Harry is that it is an infinity symbol. Coupled with the odd script in the circle around this symbol, I’m reminded of the glowing, unrecognizable (to Harry) writing on Demonreach tower when the skinwalker approached.
Overall, the cover appears to me to be Harry gathering all his powers and support. Glowing “sparks” are the little fairies Harry employs for pizza rations. He has his amulet (belief in magic and talisman against Rampires), presumably with the gem in the middle. Although they look more like stalagmites or crystals, I think the shapes around Harry are ice crystals (winter knight). The runes represent his wardenship on Demonreach and the support of Alfred. Hate to say it, but the staff may be glowing with hellfire. Why would Harry need all his powers and support? I don’t know…
