Complex sentence: The Book of Twilight, which the girl gave to Orca, activates and gives Kite the Twilight Bracelet, which uses Data Drain on the swordsman, allowing Balmung to kill it.
Split into simpler sentences: The Book of Twilight, the item that the girl gave to Orca, activates and gives Kite the Twilight Bracelet. The Bracelet uses Data Drain on the swordsman, allowing Balmung to kill it.