This manga has a really intesting plot, very usual in 70s western sci-fi and i had yet to see it's presence in japanese works.
Somewhere in the 70s when ecological worries started to come up - ozone depletion, pollution, extintions, etc; the very prolific sci-fi community took these subjects and exacerbated them into apocalyptic proportions and came up with a solution. This solution took notions from the space race and computation:
Earth eventually becames inhabitable and the human race has to go into space and find new planets to colonize, it's also frequently present in these works of fiction a longing for Earth, even when adequate planets are found. No planet is ever as blue as Earth.
To Terra is about that longing, and this longing implies a greater longing, it's actually about a longing for humanity. In Terra, when humans leave earth, to allow it to heal, they also give up free will. They admit that humanity is flawed and unable to choose the right path, and submit to a computer, that makes good choices for them. That system is called SD - Superior Dominance.
This means total submission and repression, wich is actually the true theme of To Terra. This manga is about those who are unable to accept repression, question the system, long for an ideal and fight for it.
On To Terra, children are born in vitro, selected by the computer, and then raised by professional parents. When a child reaches 14 he becomes an adult, it's the moment when the major repressive action is taken. The adult exam, wich consists in deleting all past memories. Gifted children carry on to become leaders, the rest just become obedient members of society.
As a child is being tested for adulthood, there is a chance that a flaw is found, this means the child is Mu. The Mu are humans with frail constitutions but special mental powers. They are able to resist the brainwashing and are the only ones opposing the system. Because of this they are pursued by Superior Domination.
The story begins as the main character Jomy, a particularly lively and clever boy who is about to take his adulthood exam. He had already been detected by the Mu (which are literally an underground organization) as a potentially powerful Mu. Jomy is indeed powerfull since he posesses both strong mental powers and a healthy and strong physical body. Jomy becomes the leader of the Mu and takes over the mission of returning the Mu to earth, something that, also means fight for the right to coexist within the human society.
The notion that the Mu, the rebellious agents are created by the repression process itself is very interesting and cleverly explored. The issue of acceptance of the Mu by the humans is also quickly resolved as repression and rebellion are somewhat incompatible and nimbly turns into a fight not for the freedom of the Mu, but for the freedom of Humanity.
The art is compelling and there are several brilliant spreads depicting space battles, massive computers, and particularly, telepathic action (something like an astral/abstract plane).
It also has an unusually high amount of characters, without making the action or plot confusing.
Strangely, the antagonist, Keith, at some point becomes more interesting than Jomy (Jomy himself realizes this), and has big development since unlike the Mu, he is the epitome of Superior Dominance and yet he is able to question the system from the inside.
The pacing sometimes feel a little off, but I believe it has to do with the familiarity that exists today with most of the concepts present in the manga. A lot of this stuff had so much impact in the 70s that they became tropes, and don't cause much surprise and engagement when read today.
