Not very well known or popular, Jyu Oh Sei is a hidden gem. A relatively short anime, this series went way beyond my expectations in nearly all respects.
Story
Jyu Oh Sei dispels the myth that a series has to be long in order to be good. It's only 11 episodes but the plot moves very fast and a lot of stuff happens at a good pace.
The story starts off with two twin brothers barely into their teens abandoned on a prison planet after their parents are killed. It begins as a "survival tale" with Thor, the elder brother, being the protagonist, and swiftly transitions into a nature documentary, action movie, drama and finally space opera. Secondary themes like genetics, social order, politics, relationships and existentialism are explored. You won't be bored.
Characters
Real. Fascinating. Relateable. Even Machiavellian. Everyone has an agenda. Nobody is stupid. A few wear their hearts on their sleeves but they're all well fleshed out. Even those with relatively little screen time are important to the story. There aren't really any unnecessary characters. Even the plants in this show are their own characters.
Art/Animation and sound
The animation is not as crisp in some places but overall quite good. When they say the main charater looks good, it's because he really does look good. The characters age and again this is very well done. Backgrounds are very detailed and realistic. Both the Opening and Ending themes fit the anime and were good songs in their own right. Sound effects were pretty good too. Overall very good.
Enjoyment
Extremely enjoyable. When it ended I wanted more. This could easily have been 24 or even 52 episodes.
Overall
Completely underrated but very good, very watchable anime. It's hard to find though. Please PM me if you want it, I will figure out how to make a torrent for this if only to share this with other users.