So it befalls on Globe to defend the Earth against them, and one boy gets caught up with it all -- he ends up riding a so-called "impacter" to intercept the space-fighters of the vampires. He is aided by the "Intercept Fraction", who want to intercept and defeat the vampires, but there's also the "Ark Fraction", who want to load up a big spaceship with specially selected people in cryosleep and flee the Earth to start over somewhere else.
Does that sound confusing? It kinda is -- at least, to me. Maybe I missed some vital exposition, or maybe the background is much deeper than is shown. But on another level, it is a typical mecha anime where a bunch of teenaged kids have the fate of the Earth riding on their performance, and it's a competently executed series. There's a good focus on the relationships between the kids and how they deal with the pressure and the danger. We enjoyed it.