In the story of the Night, Kuon stands as the root of all evil.
He is a Re-Birth--said to be the strongest form of existence.
Kuon has lived for 500 years, wielding the inexhaustible power of the Night; now, he aims to bring an end to the world.
Long ago, Kuon and his sister Linne were charged with protecting the Power of Sealing.
However, the immense power eventually consumed Kuon, and he lost sight of himself.
Now he desires further power--which he can attain by seizing the other half of the Power of Sealing possessed by his sister.
Kuon's arch-nemesis fled beyond the Night. By taking Linne's power and breaking the wall of the Night, Kuon hopes to reach him.
The resulting destruction of the world is merely the means to that end.