In an attempt to colonize Mars, 21st century scientists tasked with terraforming the planet seed it with a modified algae to absorb sunlight and purify the atmosphere, and cockroaches whose corpses spread the algae across the planet as they feed.

Five hundred years later, the first manned ship to Mars lands and its six crew members are attacked by giant mutated humanoid cockroaches with incredible physical strength, later labeled "Terraformars"; the crew is wiped out after sending a warning back to Earth. Decades later, a multinational expedition is sent to exterminate the mutated bugs and take control of the red planet only to be vanquished as well, except for two survivors who manage to return to Earth, one swearing to return and avenge their fallen companions. As a third expedition is assembled, questions are raised about the true origin of the Terraformars and their connection with a deadly virus afflicting mankind.

To fight the Terra formars' strength and agility, members of the second and third expedition undergo genetic modification to inherit the characteristics of other organisms, only possible after having a special organ implanted with a 36% chance of surviving the surgery itself.

When I saw this when the series first started streaming on CR I was just appalled and the ridiculous censorship and even found it heartbreakingly hilarious because in a show where people are split in two and bears' faces are stomped in you really shouldn't have to deal with indiscreet black circles that are there just for the sake of censoring it. However I really have to give props to CR for adding an uncensored version of those first few episodes.

Now regarding the rest of the series as it is, I can just say that this show is pretty original and fresh considering how it relies on the whole "Mysterious humanoid beings kill off the human species for no discernible reason" trope. However the the technology that humans rely on to defeat the Roaches (I'm gonna say "Roaches because Terraformars is just a mouthful) is something that I personally haven't seen much of in other series.

Overall this series needs another season or 2, at least so that there can be some sense of closure, get to working on it Japan

This anime can be overrated if only they wouldn't put so much flashback. I think. Also censored