Few more details about the expansion from a Miyazaki interview with Famitsu today
* The expansion story takes place in the base game's timeline, there is no time travelling into the past or future
* Miyazaki describes the story as: "Here, you are following the footsteps of Miquella who headed for the shadow lands. Further, there are NPCs also following after Miquella. The story of the DLC is told through them, and they cross paths with the player, sometimes as allies, sometimes as enemies. Also, one other main pillar of the DLC story is the history of this shadow land and the history of Queen Marika"
* Are there new weapons, magic, or incantations?
Miyazaki: Yes, many weapons, spells, weapon arts, etc. have been added. They are one of the main selling points of this DLC.
Especially weapons, there are 8 new weapon types added. Of course, there are additions to existing weapon types as well.
Famitsu: 8!? There are a great number of weapons in the main title, specifically what kinds of new weapons are added in the DLC?
Miyazaki: First of all, there are fairly classic large Japanese katanas known as "Odachi", and others are reverse-hand swords "Gyakute ken", and more peculiar, highly novel ones. For example, martial arts if you imagine monks, or dual offensive/defensive "Dueling Shields". Or throwing daggers that change all attacks into throws. So it should still be fun and refreshing for players who have gone through all the weapons in the main story.