11-nin Iru!

a lot of people don't know Kanata no Astra is a kind of homage to 11-nin Iru! many of the same characters, similar premise about kids training to fly into space end up on a ship and have to learn to cooperate to achieve their goal. Astra is a full series from a longer manga (11-nin Iru! is a one shot iirc) so can go into more depth, but if you like Astra, this movie is worth checking out. vice versa of course  

A bunch teenagers being thrown onto a mysterious space ship, and they found out their way surviving. Trust, betrayal, friendship, angst shown under various situations. They were 11 deals only with internal conflicts, being a 90 min movie a lot development has to be cut short. Also rewatchability is a bit low when you get spoiled at the end resolution. Infinite Ryvius being a 26 episode TV series, has a lot of time to develop its plot, and characters, despite the casts are huge. Teens in this series have to deal with outsider attacking and internal conflicts, so the story seems fuller than They were 11. 

Who is the traitor? For both series this is the major question that the main protagonist seeks to answer, but there aren't many series I know of, at least of this time, which cover this theme specifically. Sure, there are other series which have 'who is the traitor' in regards to one of dozens of mysteries which compromise the entire series, but for this the entire plot for the movie or the season is the 'who is the traitor' plot. With both series there is also a wide cast of characters and a lot of tension. 

The series are space opera which fall into the horror category, leaving the viewer on edge the entire time as the vacuum of space and what might happen holds its own level of horror in additions to the horrors which wait inside the places which are supposed to be safe. 

Both are sci-fi shojo from the 80s that take place in space. Terra e... is more epic in the scales of setting and time while They Were 11 takes place in a single space ship with fewer characters over the course of less than 3 months, but space, drama, and mystery all take the stage in both series. 

Crew of a spaceship encounter a problem that makes them turn against each other, suspecting fellow crewmates as the viewer tries to guess which of the characters is the true antagonist. 

Sci-fi shoujo anime is rare, but at least what does exist is pretty good! While They Were Eleven! and Jyu Oh Sei are works from different decades and there are many stylistic differences, they're solid classics of the genre. Both have intricate worlds despite their short lengths, and their similar focus on character relationships just as much as battles or adventure will make them appeal to the same audience. 

Both have simular plot about space travel and mystery of an extra person among them. 

Incredibly well crafted Sci-Fi, grounded and believable characters, two extremely underrated pieces of the mid 80s. 11-nin Iru! is more lighthearted, mystery, romantic drama. In contrast to Space Fantasia 2001 Nights' space exploration human drama. Both are definitely wort the watch for fans of Sci-Fi or older titles. 

A very similar set up - a group of strangers awaken in an unfamiliar place. Mystery abounds. 

Reaching space is often seen as a dream come true, yet in both of these movies we learn that actually isn’t the case. Both movies showcase a darker side of space travel, some of the horror aspects, and they’re older movies as well, for those looking for some of the more classic pieces. 

A lot of science fiction falls into the trap of assuming that gender roles will work the same way even on settings that are completely different from our own reality. Simoun and They Were Eleven! both reject that assumption, giving their characters an opportunity to chose their own sex at some point in their lives. Each anime ends up doing pretty different things with that idea, but if you're interested in anime with some playing with and commentary on gender in an unreal setting, you'll probably enjoy them both. 

Both Akira and 11-nin Iru! are movies from the 1980s with Akira possibly being one of the better known series, and 11-nin Iru! a more obscure piece people may not even realize exists. In regards to the time period, both pieces represent the movies of this time period quite well, yet also the fears of the Japanese people had regarding the Cold War era. While the connection of Akira to the Cold War era is more recognizable, the underlying fear still crops up in an ambiguous manner with the common theme of war and strife. The style of animations is dark, the themes moody and angst ridden, with the deep seeded feeling of doom running through both pieces in a manner which is deep. read more 

Space is the final frontier, yet is that a good thing? Both of these series explore the idea that things aren’t the way that one would expect. In that, the space opera movies feature a dystopian society, one where the main characters want to win back some level of control, but is winning back control in the way they want a good thing?