I am seriously starting to think that Demon's Souls, Dark Souls, Bloodborne and Elden Ring are the same universe. All of these games have the same themes of Dark, Light, Fire, Chaos, Souls, Blood and primordial trees.
Dark Souls 3's DLCs were all about the blood of the dark soul and its relation to humanity much like Bloodborne. The Dark Soul drives people mad and contorts them into beasts (Artorias, Manus, Gael, Oolacile creatures). In the DLC we take blood from the Dark Soul to finish a painting that is supposed to be a new world. So at the conclusion of Dark Souls 3's DLC, we create a new world from the corrupting blood of the Dark Soul. Bloodborne is (superficially) all about blood and how it corrupted humanity.
The endings for Elden Ring match the endings for Dark Souls (ushering in an age of godless dark and continuing a hopeless age of light). Rings of light surrounding dark are a symbol representing the Dark Soul and are branded upon every undead. A similar ring of light (the Elden Ring) represents the Greater Will in Elden Ring.
I think the Elden Beast, the Great Ones and the Old One share some sort of relationship. God sent the Old One, the Greater Will sent the Elden Beast, and something sent the Moon Presence.
The first flame in Dark Souls seems to have some sort of desire to persist despite humanity's desire to end the Age of Fire. The Greater Will wants Tarnished to continue the age of Order. The moon presence has some desire to continue the Hunt.
What the fuck is the Darkmoon? It seems to be one thing that is referenced in every game. Maybe the moon ties everything together. The Darkmoon Greatsword also appears in every game, but unlike Patches or the other easter eggs, Darkmoons seem to have lore significance in the games that they appear in.
I think that the Greater Will, The First Flame, and Demons' Souls' God are the same entity and they are in some sort of struggle with the Darkmoon.