Yuji Kaido has been frozen since 2009 after being diagnosed with a strange and terminal illness to be awakened after a proper cure for his disease has been found. He is awakened to the year 2031 to a world that has been completely taken over by a giant insect-like species known as the Blue. He and Marlene Angel must find a way to survive onslaught after onslaught of the Blue and make it back to a space station called Second Earth, where Yuji must discover the true nature of his condition. In many ways it is a Fish out of Water plot, but without the humor as Yuji wakes up to a world completely different and is at first unable to cope with a world in which the Blue have taken over. He does quickly learn to fend for himself, but is still shocked by how the ethics, morality, values, and general outlook on life have changed so radically since his time. For example, sex is meaningless pleasure, and there's no point in forming close meaningful bonds because Anyone Can Die at any moment. There is no longer any value placed on human life as every individual human is considered expendable.The premise is similar to that of Starship Troopers but without the campy satirical feel of the film or the political ideology of the novel. Unlike most anime, Blue Gender has very little humor and cuteness is nonexistent, though there is plenty of fanservice and other sexual moments (most of which has been censored when aired on Cartoon Network's Adult Swim line-up). The series generally has a very dark and cynical tone; however, the series does end with the message that humanity can live happily (Provided they live in harmony with the Earth).The series has very in-depth character development on the parts of both Yuji and Marlene, who end up being completely different people by the end of the anime's 26-episode run than they were in the beginning.
Anyone Can Die: Most supporting characters end up not lasting more than a few episodes, if that. Of the six supporting characters introduced in the first episode, four were dead by the end of the second, three having died within a minute of each other.
Babies Ever After/Happily Ever After: Yes, despite the overall tone of the series, it does end on a rather happy note for the main characters. Yuji ensures that the threat to humanity is over, and then reunites with Marlene, with the promise that they can live a happy life together on Earth. And Marlene is pregnant with Yuji's child.
Bug War The Blue are more or less created by the humans, in fact, because humans wanted to use B-cells for war.
Celibate Hero: Interestingly, despite the attitude towards sex and love in this world, both times Marlene is presented in such a situation prior to having sex with Yuji, the male involved in the situation only gets so far as groping her before she stops them from going further. In the first occurrence, she's not in the mood. In the second, adding to the previous reason, by that point she'd fallen in love with Yuji. Additionally, this may be in part due to her backstory, in that she was forced to discover about such things at an unfortunately young age, and ended up deeply hurt as a result.
Cold Sleep, Cold Future: Most of the characters here are heartless bastards who place little if any value on human life to the point where civilians who are not granted access to Second Earth are not only expendable but are pretty much considered dead to those who are on Second Earth. The one and only thing on everyone's mind is wiping out the Blue, and that's it.
Common Tongue - for all the efforts at realism, everyone living in the future speaks the same language, no matter how geographically isolated.
Cryonics Failure - This happens with alarming frequency. Hell, happens right in the first episode.
Deadly Dodging - In The Warrior Marlene kills two Maneaters (praying mantis-esque Blue) by evading their attacks and causing one of them to impale the other. She skewers the second one with her bayonet at the same time.
Deadpan Snarker - All of the main characters and a fair few side characters have their moments...
Foreshadowing: The last couple of episodes include a few hints to how the series ends out. In the 24th episode, Yuji and Marlene, after finally admitting their feelings and having sex, are shown transparent in a naked embrace against the Earth, signifying the new life they promise to live together at the end of the series. In the 25th episode, Marlene is shown acting much more passive than she normally does, and in one scene, watches a group of settler children play whilst resting a hand on her stomach, before interacting with them in an unusually motherly way, hinting she's pregnant with Yuji's child.
Free-Love Future - In this story, even the act of kissing is seen as a "pre-battle ritual". Justified because humanity is on its last legs, and everybody has to get it on while they've got the chance.
Gaia's Vengeance - The Earth creates the Blue because the human race has become overpopulated and because of their negative impact on the environment.
Gaia waited for humans to make the Blue while trying to cure a disease, then directed them to kill us. Then when that fails, she kills only the Blue and drives all the humans in space insane, what a girl. So not only is she a bitch,she's lazy too.
Militaries Are Useless: This is combined with Show, Don't Tell, as it is mentioned that humanity's militaries were defeated off screen, but we are never shown or told exactly how. The humans show themselves capable of defeating the Blue without tremendous difficulty in the series, and if they were to use modern day military tactics, the humans should, by all accounts, have been able to win pretty handily.
Mind Rape - The main disciplinary tool of Second Earth. The recipient ( Marlene) is forced to watch a virtual reality simulation showing the brutal deaths of everyone she cares about.
More justified than most, as the fact that Marlene is falling in love with Yuji is a telling sign she's being humanized more and more through Yuji's influence. Her behavior comes to clash with her superiors,who are so absorbed in fighting Blue that they do not seem to be able to even comprehend what love is anymore.
Tuckerization - Yuji's friend Takashi, named after one of the producers
Stuffed into the Fridge - In the very first episode, Yuji is seen eyeing an unnamed, attractive female sleeper. It seems like she might be set to provide a companion in the future to whom he can relate, until he finds her body twisted into a Blue cocoon.
Justified in that it establishes that Anyone Can Die. And wouldn't you know, by the end of the third episode, everyone save for Yuji and Marleneis dead. Most of the supporting characters didn't even make it past episode two.
Training Montage: Yuji's training-montage contains the world's bare minimum elements for a training montage: a total zero at the start, someone correcting how he holds a gun, some guy going "hey kid, you've got a knack for this!" and suddenly, Yuji being ready to go into battle.
On the other hand, when he's "ready to go into battle" he immediately gets his ass kicked, so perhaps not a completely straight example.
Worm Sign: The reason for the Land Whale's name. It exhales while burrowing, shooting a "spout" of air and water vapor up through the sand. It sometimes causes a more normal form of the trope, disturbing the sand as it moves beneath it (though this depends on how close to the surface it is and how fast it's moving).