そしてこの宇宙にきらめく君の詩

On a world completely different from Earth people have been living in artificial space colonies for a long time.
A few colonies have gathered together to assemble a nation, the people call it "St. Folia".

The protagonist Lumina is the princess of the Shumal Kingdom that governs St. Folia.

Their power that once spanned the entirety of St. Folia is fading. The Shumal Kingdom's outlying principalities are in a state where they can't sustain themselves without help. With conflicts over the succession of princes and wars between different ethnic groups going on all the time the people are exhausted. But Lumina knows nothing of that reality, she is growing up sheltered in her own little pure world.