Blue Drop is a series of manga stories by Akihito Yoshitomi in which Earth has been conquered by the Arume, an alien race which is very much human in appearance, but consists only of females. Consequently, they are by and large homosexual and are attracted to earth women, which leads to a lot of depictions of lesbian sexual behavior. An anime series was released in 2007 that takes place one thousand years before the manga and describes the events leading up to the Arume invasion. The anime's emphasis is more on character development, whereas the manga tends to be more explicit and often crosses the line towards Hentai (although it's generally more creepy than erotic).The manga consists mainly of one-shot stories, presented in two series, describing the struggles of human society with the Arume in charge. The main recurring character in the first series is Yui, who is a human/alien hybrid and a member of the earth resistance. An important theme is the Arume's use of children to fight the semi-sentient remnants of their biological weaponry in the earth's seas. The second series , Blue Drop - Tenshi no Bokura (Angel's Men), adds some gender-bending to the mix and often contains very graphic (and very horrifying) sexual scenes and themes. Blue Drop's third manga is a short, romantic story called Maiorita Tenshi which chronologically is set between the anime and Tenshi no Bokura. Lastly there is the mangaTenshi no Itazura (Angel's Prank), the shortest Blue Drop work being only three chapters in length.The anime series is called Blue Drop - Tenshitachi no Gikyoku (Angels' Play) and describes the antics of Hagino and Mari. Hagino is the commander of an Arume battleship; Mari is the sole survivor of a disaster caused by that ship five years earlier. The story focuses on the gradually intensifying relationship between the two girls, set against the threat of the Arume invasion and Hagino's rising doubts about its purpose.The subbed version of the anime currently has a free legal stream on YouTube courtesy of the animenetwork, although restricted to certain countries.
Bittersweet Ending: The anime ends with Hagino pulling a Senseless Sacrifice at the beginning of the Arume Invasion. The Arume win. However, the Distant Finale 30 years later implies that humanity is on its way to a truce with the Arume.
Blue and Orange Morality: The Arume aren't completely out there, but their sense of morality definitely doesn't jive with humanity's. Specifically, using Child Soldiers (Volunteer, or so they claim) for suicide bombing because it's "beautiful" and being grossed out by males.
Book Ends: The anime starts and ends with Michiko in a shuttle on her way to a peace talk with the Arume.
Crapsack World: If you're a Magical Girl, you're a bomb disposal unit. If you're a schoolgirl, you're little more than a sex slave. If you're a guy, you're used as a lab-rat for transgender experiments if you're lucky.
If you're not so lucky as to be part of an experiment, you're an animal, a third-class citizen treated like freed Africans in Antebellum America- not a slave, but only just.
Evil Versus Evil: In Tenshi no Bokura. The Arume (simply batshit insane) versus Yoshimura (batshit insane and concertedly sadistic). Weirdly, they seem to be at peace by the end despite wanting to wipe out each other's sex.
It should probably be noted that there are hints that Ma-chan and Yoshimura are actually doing a tag-team plan. This actually may qualify as Fridge Brilliance as this does seem altogether too likely be the only way to restore the Arume's men without a certain segment of the Arume throwing a Spanner in the Works.
Gender Bender: In the manga Tenshi no Bokura only. Played for drama, tension, and horror rather than laughs, then turns into an subversion- its just a girl brainwashed to THINK she had once been a boy.
Not so much as "think" she was a boy. The girl had the boy's memories and personalities downloaded on top of hers, and over the course of the series, their minds kinda blended together making a new one with the boy's personality being dominant.
Hot for Student: When the Arume run schools, many of them seduce their female students. In Tenshi no Bokura, they had a school that was, essentially, their seraglio, the girls having pretty much been raised to think that such was the norm.
If It's You, It's Okay: In the original Manga, Ami feels this away about Yui after Yui rescues her. Also subverted in Tenshi no Bokura with Kotoko, who thinks she can fall in love with Shouta but can't get past the fact that he's a guy.
Jumping the Gender Barrier: Tenshi no Bokura, which does it with a technically heterosexual couple due to lesbianism and a male mind upload into the girl- the barrier is jumped when the upload starts wearing off.
Mars Needs Women: As if the Arume didn't have plenty already. To make matters worse, Tenshi no Bokura reveals that they actually need men in order for their species to not die out in the near future. They even invaded for the sole purpose of getting our men. Then they got cold feet at the last minute and took our women instead, as they are much hotter albeit useless for stabilizing the Arume population dynamics.