Complex sentence: After her sister Serah is declared an enemy of Cocoon, Lightning attempts to save her: she and others are then chosen by the fal'Cie, a divided race of demigods who rule the worlds of Gran Pulse and Cocoon, to destroy Cocoon.
Split into simpler sentences: After her sister Serah is declared an enemy of Cocoon, Lightning attempts to save her. She and others are then chosen by the fal'Cie, a divided race of demigods who rule the worlds of Gran Pulse and Cocoon, to destroy Cocoon.