Alien 9

Both seem to have a cutesy art and all, but in reality they are much darker and cruel. Things like underage girls communicating with alien life forms and getting strange powers as a result. 

Alien 9 is like a compact version of evangelion. Both deal with characters that are stuck with a duty they aren't comfortable doing, their own insecurities keep them from performing well under pressure. The premise is also similar, a city/school are being invaded by extraterrestrial forces.  

Both of these series have a cute exterior but are darker at heart. They also have a similar feel to them and involve young girls/children and alien-like creatures that fight.  

Both have alien beings that form respective parasitic/symbiotic relationships with humans, the way these humans combat each-other is very reminiscent. The metal screw type protrusions of alien 9 as well as the bladetype things of parasyte and the way they are applied in battles are very similar. Both involve the main character entering this relationship with the alien against their will.  

both shows mix horror elements with slice of life. gakkougurashi is about high school girls trying to survive a zombie apocalypse whereas alien 9 is about elementary school girls fighting an alien invasion. 

Both are OVAs that use symbolism to convey a coming-of-age story. 

Yuri and Tsubasa are both very similar. a) They are child main characters with not the same ages but yet very similar ages. b) They both have supporting characters to help them conquer their difficulties. c) both have to fight aliens or enemies as little kids. It's their importance. d) both cry a whole lot especially of dangerous things. These anime both came out in the same year but I'd have to say Figure 17 was slightly more of a darker theme than Alien Nine, which contains more uncomfortable stuff for children more than Figure 17. 

Alien Nine has the same theme of grade-schoolers capturing aliens but with a more serious and slightly darker storyline. 

Cute and innocent character design of the main characters but these shows can be serious and mature. Similar age of main characters. Monster design is really good and unique in both series. 

We have children who interact with and use alien life forms for fighting; both are somewhat abstract and experimental. 

Phos and Otani are very similar characters: useless is best word to describe both of them. In Houseki no Kuni we can see rapid development of Phos character as she has perfect environment to grow. Alien 9 depicts same type of person in imperfect environment. Along with environment Phos is more perfect and likable because she is useless but also cheerful. Otani is useless and a crybaby so you can find her annoying sometimes. Set of characters differs in quantity but in both shows we've two types of characters (excluding protagonist): Sensei (caring in Houseki vs. exploitative in Alien 9) and friends (leading vs. replacing her in her duties). Both shows are weird but each has different kind of weirdness. In short (lol wtf vs. wtf... WTF) read more 

Two violent OVAs with deceptive aesthetics. Alien 9 looks like some sort of cute slice of life/mon show, but it ends up getting about twice as dark and weird as Neon Genesis Evangelion. Apocalypse Zero seems to be nothing but perverted grimdark ultraviolent schlock, but at heart it's an idealistic homage to Kamen Rider with black & white morality and an impossibly noble protagonist.  

Two totally happy moe anime with cute girls doing cut... WHAT THE HECK DID JUST HAPPEN RIGHT NOW?! It's a rare ocassion when a horror anime manages to actually disturb and scare people, but these two anime manage to disturb you VERY well. 

Both have very surrealistic atmospheres and go about the everyday lives of citizens. Both also deal with paranormal phenomena and come to rather odd conclusions. 

Both shows take heavy inspiration from Evangelion and feature young characters feeling lost in a supernatural world. The environments remain relatively mysterious throughout each show to instead focus on the feelings of the main characters and how disjointed they feel to others and themself. Both have an unusual art style and a dark tone.  

Both have similar aesthetics of cute girls dealing with intense surreal situations. They both have very disturbing times as well as happy times and the overall shock of the characters going through there lives because of what is happening is similar. In another point both of the main characters are very similar in there hesitance to fulfill there destinies despite what all is going on around them.  

Both have a surprisingly similar feeling! They have that old 90s- early 2000's look, use a surreal method of storytelling, and require quite a lot of time outside of the anime thinking about what you just saw and dissecting what messages can be drawn from said surrealistic scenes.  

Both Alien 9 and Akira provide for a semi-humorous but dark delve into human psychology when dealing with otherworldly and unfamiliar conditions that both play into the sci-fi category. Both have a semi-futuristic society as a setting, and both have a very surreal feel, especially with their unique twists on storytelling. Also, both anime were made in the early 90s / 2000s and have unique art styles that really makes them enjoyable visually as all heck!  

Nobody outside of the main cast seem to have a grasp on reality. Excess of similarities in shot composition, similar environments and locations. Ethereal. 

Both shows about girls who have to fight Both shows about friends who bond over being put into odd circumstances Both dark twists off the magical girl genre 

The main trio of girls have very similar chemistry and almost the same personalities. One of them is calm and composed, the other is active and unashamed, and the main character is reserved and is always afraid to fight the monsters. Each takes a different approach to their tone and the seriousness of each battle, but both are basically monster of the week shows, while diving in to romance (UG) and the psychology of the characters (Alien 9). 

Both have a moe aesthetic with child like designs and big eyes. And in these two there is a gray tone in the plot, in Alien 9 the psychological topic and In SSR the cyberpunk background. Both have a existencial tone in the development. 

Both series have a young girl(s) as the protagonist who has to befriend an alien who will help them battle the forces of the evil aliens. Both are also in a very cute stye that leads people to believe its a light hearted anime but both have dark, sad, and realistic elements to them. 

The vectors are very similar to the borgu's attack. As the Azumanga-esque art style would suggest, Alien 9 is not quite as dark as Elfen Lied, but it can still be fairly bloody. 

Both take place in a school setting and have similar character art. Both have bizarre situations based on the sci-fi elements in Alien Nine and the overall comedic elements in Azumanga Daioh. If you like the weirdness in either one, you should watch the other.  

Both deal with a group of children thrust into dangerous and traumatic situations because they have been "chosen" to protect their world.  

Both feature young main female character crybabies. Yet they are airheads and have fear of battle. 

Alien Nine reminded me of Haibane Renmei because of the level of bizarre and weirdness each of these shows contain. Both are out of the normal comfort zone, and have a slice of life with an interesting sci-fi twist.  

Both anime feature extreme horror-themed violence, and both plots consist of a series of attacks by monsters which must be repelled by the series' respective heroins. Beyond that, they both feature very similar plots and general atmospheres with dark, overarching mystery-conspiracies that are slowly revealed over the course of the series. I would go so far as to say that Blood-C appears to have been very heavily inspired by Alien 9, but I cannot find a source that supports that claim. 

Cute girls killing cute monsters. Bright, colorful characters and color palette. Lots of pastels everywhere, it's a visual feast. If you like one you should at least try out the other. 

Alien 9 is similar to Musaigen no Phantom World in it's main plot setting. In Alien 9 they are in a school club that fights aliens off their school grounds aided by Borg their alien helmets, Musaigen no Phantom World is also about a high school club that fights phantoms and use their special powers to their advantage. Though each show has a very different tone, Alien 9 is much darker and physiological whereas Musaigen no Phantom World is much more lighthearted.  

Both series are a dark turn on the cute and moe genre that goes badly for the main characters, who are in both shows young girls. Both have a weird structure and plot twists and have unsatisfying endings, so its very likely that you will apreciate the other if you enjoy one of them. Also they are both extremely well done and dont give a damn about what the audience will be expecting.