Nintendo has posted several new trailers for Genei Ibun Roku #FE, showcasing recently revealed characters and mirages, as well as an introduction to the main protagonist, Itsuki Aoi. The longer overview video outlines the opening premise of the game, and you can also see characters like Mamori in action alongside their Mirages.
Check the footage below, which has new both new cutscene and combat gameplay.
Character Introduction - Itsuki Aoi
Mirages and Mirage Masters
Genei Ibun Roku #FE launches in Japan on December 26th. You can find details on the Japanese release and special edition here. A localized release is set for 2016.