We already knew from Birth by Sleep that Eraqus and Xehanort go way back. Now, we're getting a look at their (admittedly adorable) days growing up in what we presume to be the Land of Departure. We already got a dose of the weirdly-hot young version of Xehanort through his older form's time shenanigans in Dream Drop Distance, but this is the first we're seeing of lil' Eraqus.
The trailer opens with them discussing the Keyblade War in an apparent continuation of last year's trailer. When Eraqus plays dumb about the "lost masters," Xehanort calls him out. How long has Eraqus known about Xehanort's ambitions? And why did he forgive him before the events of Birth by Sleep?