I’ve seen a tiny scan of the Dengeki article on ClaDun 2. It seems that the characters that will be showing up in it are:
Lloyd Bannings from Zero no Kiseki
Tio Plato from Zero no Kiseki
Lilia from Ys II
Adol Christin from the Ys series
Dogi from the Ys series
Estelle Bright from Sora no Kiseki
Joshua Bright from Sora no Kiseki
