What if the world of umas is a simulation in which the brains of top horses get attached to a super machine to simulate the anime and game's world? Think about how the fake and bland the humans feel without some exceptions like the trainers, who were designed especially to cater to every needs of their trainees. Or how there might be (((magic))) or not.
And what if the apparition Manhattan Cafe sees that no other umas can perceive is the ghost in the machine, an echo of the real world that they can simply not understand, but desire to reach in order to become real horses again.