The Cross Shuriken is DEFINITELY a phantom weapon. It's listed as a royal arm in the build a lot of press outlets played for chapter 1, but that's not all.
The figure on the far left is wielding it. To me, this not only confirms the shuriken is one of the relic weapons Noctis seeks, but that the figures in the clouds (are representations of Lucian kings of the past.and the figures Nyx summons in Kingsglaive)
This was basically my theory
The phantom weapons Noctis can control/use are from the figures we see, any other are just generic ones for the limit break mode Noctis has.
So Noctis will have a Trident Spear at one point and whatever that One figure next to the suriken guy is holding.