Tsutomu Nihei

A thousand years after the destruction of Earth by gigantic aliens called Gauna, mankind is living on massive spaceships. One of these space ships is Sidonia, which is protected by large pilot-controlled exosuits called Gardes.

The story takes place in a city where it's said that has thousands of levels. In a shutdown area, thousands of levels overlap each other, you couldn't tell the sky from the ground and you couldn't tell which way is up or which way is down. Maybe the original purpose of this story is to unravel the mysteries bound in this time and world. For the humans who found this vast rare multi-level city, the mysterious main character "Kirii" wanders to search for the "Net Terminal Genes" that were not infe (myanimelist.net)

In the distant technological future, civilization has reached its ultimate Net-based form. An "infection" in the past caused the automated systems to spiral out of order, resulting in a multi-leveled city structure that replicates itself infinitely in all directions. Now humanity has lost access to the city's controls, and is hunted down and purged by the defense system known as the Safeguard. (imdb)

A world blanketed in an endless and ever-growing ocean of snow. The people eke out a living, either huddled around the roots of enormous trees dotting the surface, or high in the canopy, which spreads over the planet's atmosphere. (imdb)

It’s been nearly 10 years since ace pilot Nagate Tanikaze repelled the Gauna forces and saved Sidonia, humanity’s last home. In this final battle where annihilation looms and love blossoms unexpectedly, humanity will either persevere or find itself dominated by the Gauna. (animenewsnetwork.com)