[warainagara]

Spoiler for a suggestion about Simoun's main theme (1), a long and boring post about Aaeru and Neviril's choice:

The catch phrase appearing in the official website is from ep 1,

"Let's go where we can be free,"

Neviril's line to Amuria during a battle.
That was ridiculously out of the context, since they were fighting with enemies and had no time to talk about freedom thing.
Did they really want to escape the battle by going to Tempus Spatium's side or else?

After ep 1, their conversation has been forgotten, but since the idea of going to the different world has got substantial, it seems to have more significance.

Technically, Aaeru and Neviril want to evade gender choice to go to a different world.
The other members of the Chor Tempest see such an attempt in their own views, but one thing noticeable is that they might not expect a practical change of the nation they live in.
Rather their longing seems to be something transcendent and conceptual.

"Simoun is shoujo(girl)." (Onashia in ep 24)

As a result of the defeat, Kuukoku had to be deprived of the access to all the Simouns and the girls had to go to the Spring for the rite to become adults.

Simoun, the craft of the gods, is both a religious symbol of the theocratic society and the cause of the war.
And the girls have had various connections with Simoun and the Simoun war, as "shoujo."
The fact that the access to Simoun was blocked would be associated with another fact that the girls are no longer allowed to be shoujo and should be prepared to get into the ordinary world.
And the way to get into the world is to "become a man or a woman as others in the sociery have done."

"Getting old means repeated choices and repeated choices mean the elimination of possibility." (Aaeru's grandpa, ep 18)

Not only growth but also numerous facets of socialization may be implicated in his words.
We call the process of getting accustomed to the fixed and imposed way of life "socialization."
And after the process, one more member of the society is born, who has few options at hand and is surrounded by the ordained social expectations like gender role, heterosexuality, a set of morality, contribution to the society as a family member and a career person.

The Eternity admired by the Chor Tempest would be about the pristine status free from the rein of society.
Also, the freedom Neviril unwittingly mentioned would be the restoration of individuality that might have been oppressed in the standardized life.
It may be that Aaeru and Neviril opted to confront such a social demand by choosing not to choose gender.
By journey on Simoun for a different possibility, they would accomplish the true Aaeru and Neviril, not the Aaeru and Neviril who lived in a specific era of Kuukoku.