If you're looking for manga similar to Chrome Shelled Regios: Legend of Regios, you might like these titles.
Many years after a devastating war, Earth is now being watched by a group of beings known as The Third, named for the third red eye on their forehead that can access various computer systems. Navigating this barren, apocalyptic landscape is Honoka, a jill-of-all-trades who uses her powers to keep her friends from The Third's deadly grasp.
Earth after World War II. Rebuilding after the destruction has given rise to various vices. Disposers roam the cities cloaked in shadow and mystery. Kaede is a Disposer of SA rank, the highest level a disposer can reach. But he has to be in Central City, he must find the one who murdered his father...at any cost.
The near future. A terrible battle against a parasitic virus called "Gastrea" has been fought...and lost. Humanity is cornered and lives in despair. Rentaro and Enju face constant danger in their work as a team of specialists working for the Tendo Civil Security Agency, one of several groups dedicated to fighting Gastrea. Enju is one of the "cursed children," who survived the virus and gained superhuman powers as a result. A crazed top-hat-wearing terrorist is on the loose, but Rentaro's got his hands full just dealing with his fellow civsec agents!
After being diagnosed with a mysterious disease, Honoka Kusakabe was put into cryostasis by the scientist Heitarou, her father. However, when she awakens it is not to her family’s loving arms – she is greeted instead by a barren world filled with vegetation and not a single human in sight, save for a dog-like robot named Haco. With his help, Honoka learns about the new world around her and searches for the answers she seeks.
Long after the fall of humanity, the world lies in ruin. Factions of autonomous war machines, monstrous biological weapons, and other horrors of a bygone era battle it out in the remains of the society that created them, their conflicts endless and seemingly meaningless—until, that is, a machine finds its own meaning in the form of a human child. That machine, Humanoid Mobile Weapons Unit Number Ten, develops a fiercely protective bond with the child, and soon the two of them set out on a journey together. Their mission: to search for other human survivors, to deliver the child to her people...and to enjoy the trip for all they’re worth!
Scientists predicted an imminent meteor impact on Earth that would annihilate civilization, but contrary to their prediction, the meteor missed Earth. Though avoiding immediate destruction, humanity found that the meteor left behind something in its wake, something that would change the course of civilization forever: a new form of bacteria that ate through all known metals. Facing this new era where all metals turn to ash, Jinkichi and his classmates will have to survive with little help from the Japanese government. Some of his classmates have already begun to understand that the norms of the past have collapsed, and lawlessness will be the new law. Jinkichi will have to protect himself as well as his classmates from the violence that ensues.
Rick has lived a normal life as a mechanic's apprentice in a world underground. That, however, is about to change as he bumps into a strange intruder who is not quite like anyone Rick has ever seen before. Venus, the intruder, claims to be from another world just like Rick's, though slightly different. With the police after Venus, can they figure out what is going on?