Spoilers ahead
As it is stated in the synopsis the show is about the last of humanity living in a mobile fortress that the show is named after, and defending/hunting bug like creatures known as Gadolls. Using the parts from the Gadolls as food and resources and most importantly using their blood as fuel. Accompanied by the humans are the Gears who are a strangely rainbow colored human like beings who make up most of the fighting force against the Gadolls. With Natsume, our main protagonist, hoping to join and fight alongside them, although ends up being dashed away by not qualifying. And what could have just been a bog standard show about Natsume trying to work hard to prove to them that she is capable ends up being more than that by the second episode. Because while the plight of human survival is a true reality, it is being used for the expense of other beings as a sort of Truman Show-esque MMORPG so they can have fun killing Gadolls and collect their blood that they need for survival as well.
The show ends up being split into two different plotlines with the primary one being the standard plot from the beginning about Natsume trying to work and improve herself in order to one day fight against the Gadolls, unaware (like most humans) of the greater system controlling them. While the other plotline follows her mentor Kaburagi who is part of the system and is trying to destroy it for himself and in order to stop the artificially perpetuated suffering that humans had to go through for so long. As he sort of uses Natsume to unknowingly help him due to the fact that she is an anomaly in the system. With both plotlines inevitably coming together during the final 3 episodes delivering an otherwise satisfying conclusion.
For a show that only had 12 episodes they were able to do a whole lot with it. Although one of the things that was pushed to the wayside would be character depth. Many of the side characters are two-dimensional at best. Even the main two duo of the story have simple characterization and easy to understand mentality, personality, and motivations. Of course none of this is a bad thing as many of the characters have easily likeable personalities and even the main antagonist has a weird charm to him as well.
It also helps that the show has some pretty good production values especially when it comes to it’s zero g-esque, but overall it’s just very good. The most important part is whether or not you can accept the shift in story the show is going for in the second episode. Because if you can, you’ll find a pretty decent show that’s worth watching.
