As post-launch DLC.
http://gematsu.com/2014/07/marie-playable-persona-4-arena-ultimax
"The new fighter, who originates from Persona 4 Goldens Velvet Room, will use the Persona Kaguya in battle."
http://gematsu.com/2014/07/marie-playable-persona-4-arena-ultimax
"The new fighter, who originates from Persona 4 Goldens Velvet Room, will use the Persona Kaguya in battle."