So I read this a while back. As far as I can recall, it's a very abbreviated version of the TV story (which is too bad, since books/manga can be very good at filling in holes that are left by TV pacing). Side characters besides the Deunamists, Komon, and Nagi are mostly pushed into the background or non-speaking roles.
Spoilers for the end of the series
Then Zagi explains that he predicted Nagi would be picked to be a Deunamist, that's why Zagi killed her parents, to nurture the darkness within her.
Komon saves Nagi, then becomes Ultraman and starts fighting Dark Zagi. The people see Ultraman and the memory block is erased.
Cut to TLT base for exposition. The visitors gave the technology, Lethe, to help erase/suppress people's memories. They're panicking, since they worry people will give in to the fear of the Beasts, thus making them stronger.
Then Illustrator receives a telepathic message from the Visitors. The Visitors explain that their home planet was also attacked by the Beasts. But then a giant of light appeared, Ultraman. He then proceeded to exterminate the Beasts. They explain they don't know who Ultraman is. Maybe he's a lifeform evolved to be the natural enemy of the Beast? Or maybe a god born from some ancient civilization? He saved the planet and left for the far reaches of the galaxy.
But even with the planet saved, the fear still lived in their hearts. The Visitors tried to create a guardian to protect them. An artificial life form with eternal life, Dark Zagi. Zagi could see into the future. He decided to end all the suffering, he would create a world with no life, no emotions. The Visitors decided to blow up their planet with Zagi. Weakened, Zagi used the Beasts and Ultraman to his advantage.
The first Space Beast, The One, gave humans the same fear as the Visitors. That's why they had the Lethe System for erasing the memories of the Beasts.
But people are remembering, but instead of giving in to fear, they're cheering for Ultraman. Giving him his ultimate form, Noa. And Noa defeats Dark Zagi.
In the epilogue, the Night Raiders are still fighting, but out in the open now. The breaking of the Lethe also meant that Beasts around the world had activated, so the Night Raiders are still doing clean up work. Also, Shiori is shown to be okay in this ending.
I haven't seen the TV series in maybe 10 years, so does anyone know how this differs from the TV series' story?
I'll scan this up when I get a chance.