I would be massively dissappointed if we don't get Luna (and Gentiana) as a guest party member.
Just imagine this scene: in Altissia, during Niflheim invasion, a giant snake rises from the water threatening to destroy everything, Luna is in front of it and Noctis knows it, so he rushes through the city smashing down Magiteck warriors, reaches her and a duo tag-team fight against both Niflheim soldiers and Leviathan begins.
Just imagine this scene: in Altissia, during Niflheim invasion, a giant snake rises from the water threatening to destroy everything, Luna is in front of it and Noctis knows it, so he rushes through the city smashing down Magiteck warriors, reaches her and a duo tag-team fight against both Niflheim soldiers and Leviathan begins.