Kingdom Hearts 4 Announced At 20th Anniversary Event

Sora is then shown running through the city after a large Heartless resembling Darkside suddenly appears out of nowhere

 After summoning his Keyblade, Sora takes on the Darkside in what looks to be early gameplay footage

where Sora is shown using Keyblade Transformation-esque abilities (although notably only with the Kingdom Key) against the Darkside.

As Sora faces the Darkside, the camera pans up to reveal two hooded figures

which are presumably the Master of Masters and Xigbar,

who was shown to be the Master's apprentice Luxu at the end of Kingdom Hearts 3.

who was shown to be the Master's apprentice Luxu at the end of Kingdom Hearts 3.