I get what it's telling you to do and I get that this is some kind of Full Metal Alchemist thing. But from that first thread I don't get how that guy discovered any of this, especially translating the bug jars (I've found 2) also I think it will be hard as fuck to run massacres in those major cities without dying. Also which day is this "Promised Day".
Later in the reddit comments, someone posts that they think instead of committing mass murder in the cities, you have to Kill a dragon in each of those cities.
Ok the weirdest thing just happened to me. I was thinking about that guys whole transmutation theory. And I started looking at the dragonfly jar because that's the only one I had. Need-Horse-Water is what it translates to, and he said something about whiterun being the horse head. I noticed water flowing out of the city so I traced it back to it's source, it was flowing out of Dragon's reach and into a pool underneath the bridge. Then I noticed a skeleton floating in the water there. I had seen it before, just never paid attention to it. And then everything just seemed to right. Dragonfly and dragons reach - the place where you flew off in a dragon. The horse water being the origin of the water coming out of whiterun. I put the jar in the skeleton and I shit you not a dragon started attacking the city the moment I put it on him. Nothing happened when I killed the dragon but I realized that the crests of blood may in fact be having to kill a dragon in each of the city. I dont know if placing the jar on the skeleton had anything to do with the dragon spawning, but realized that it would make more sense for Bethesda (If this whole theory is correct) to require you to kill an assortment of dragons, one in each of the five points (main cities), as well as the other locations he listed. TL:DR - For step 1, kill a dragon in each of the 5 cities instead of going on a killing spree, makes much more sense!
Also, that reddit thing i posted is just a single comment in a larger thread.