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 by Asahi Production and Gonzonote 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 manga Tenshi 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.
- Artificial Human: The Arume create synthetic children as living bombs.
- 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.
- Bury Your Gays: Hagino dies, right after she and Mari confess to each other. Who would have seen that coming?
- Cool, but Inefficient: Tsubael uses a robotic bird to commmunicate with Hagino. Cell phones, anyone?
- 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.
- Evil vs. 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.
- Gratuitous English: Hiroko's suspiciously apropos "KEEP WEIGHT" shirt.
- 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.
- Invisible to Normals: Mari is the only one who can see Tsubael's holographic projection.
- Mars Needs Women: 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.
- Please Put Some Clothes On: In Tenshi no Bokura, Admiral Mariel walks around practically naked. When Shouta asks her to "put something on", she dons cat ears but remains otherwise undressed.
- "Ray of Hope" 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.
- Show Within a Show: Michiko's play is a thinly-veiled parallel to the main story starring Hagino as Jeanne d'Arc.
- Situational Sexuality: Many of the humans engage in homosexuality in the gender segregated areas.
- The Guards Must Be Crazy: Azanael is detained after an attack, but she manages to keep a secret control device for her fighter craft, which is repaired by the ships captain.
- The Mirror Shows Your True Self: When Nagino is tele-talking with Mari, she's invisible, but Sugawara sees her as a reflection in the water.