Speculation about the lore and story of Dark Souls 3 starts now.
The Souls series of games by From Software always invite a lot of fan interpretation as to what's actually going on in their stories. These games tell stories through NPC chatter, descriptions of items and weapons, and through in-world tricks in how levels connect with one another, and other elements.
There's usually a clear objective given to you as you start the game, and it hardly changes. As you talk to more NPCs and finish more levels, you come across new information and your perspective shifts, and it's through that your version of the story comes together.
Because of this, Souls fans everywhere have taken to discuss every little bit of info they can get their hands on, in the hopes of reaching some semblance of a coherent synopsis. In the case of Dark Souls 3, fans have already started writing down notes about what the game's story is going to be about, and if the lore will have connections to earlier Dark Souls games.
I am going to list some of the most interesting fan theories so far, but before we begin, it's important to note that all Souls games share very similar themes, and each offers different takes or interpretation of them. For instance, it's easy to see some Demon's Souls elements in Bloodborne - and similarly, Dark Souls references in Dark Souls 3, without them amounting to anything.
This does not automatically mean 3's events will be based on what happened in 2 or the original, so it's best to take everything with a grain of salt until we finally get the game to dissect for ourselves.
As you probably know, The Lords of Cinder were a big part of the original Dark Souls, and rekindling the flame was your primary goal in that game. In the recent trailer, the narrator mentions Lothric, where the game is supposedly set and it's where all the lands of The Lords of Cinder converge.
The theme of the fading flame and firelink seem to have carried over to Dark Souls 3. The trailer then mentions The Lords of Cinder returning from the dead, but doesn't actually list the names of those - we know - are in possession of the Lord Souls from the original game.
It's possible the new lords are just one of the many who scarified themselves to rekindle the flame. Speaking of rekindling, the Unkindled referred to in the trailer could be players of the original game who chose not to rekindle the fire, and are therefore unfit.
One NeoGAF member sees some similarities in design between Dark Souls' Artorias of the Abyss and The Abyss Watchers. The sword, moniker, and general look could mean they're connected somehow.
One of the new lords, Yhorm the Giant, somewhat resembles the giants from Dark Souls 2. Another commenter believes the "profaned land" in question is the Giants' home in Dark Souls 2, which Vendrick and Nashandra profaned before the events of that game.
Those who played Dark Souls 3's network test remember the black substance bursting from some of the meager enemies you came across, and some believe Aldrich, Saint of the Deep has something to do with it.
Finally, there's another interesting take from this Reddit user, who suggests that Dark Souls 3 takes place during the Age of Dark, assuming the fire was not rekindled at the end of the first game.
There are still embers in that world, but none strong enough to light the flame, which could explain the strong and heavy ash we saw in the area of the network test, and in the game's trailers.
Upcoming trailers, and the game's release itself, will no doubt shed more light on everything discussed here. And whatever the game's story ends up being, the journey of putting the pieces together is one of the reasons we're fans of the series.