Arc Rise Fantasia and Luminous Arc both have “arc” in their name, but they are not directly related. The games take place in different universes and are different genres. Even though they are separate entities a few familiar faces from Luminous Arc found their way into Arc Rise Fantasia.
A Famitsu scan shows Saki and witches Vanessa and Lucia (thanks for the tip Hero of Legend!!). The trio are rendered in 3D and in the heat of battle. Are they allies? Enemies? And what are they doing there?