The Beginning of Darkness

The Beginning of Darkness is Disc 2, Track 18 on the Xenoblade2 Original Soundtrack. It plays in the following cutscenes in the main game of Xenoblade Chronicles 2:
 * Brighid eavesdrops upon Dughall as the latter plans to capture the Aegis.
 * Dughall confronts the party in the Titan Battleship.
 * Pyra urges Rex to turn Umon's ship around before Ophion attacks.
 * The party finds a dead Titan in Uraya before being attacked by the Elder Arachno.
 * Akhos confronts the party in Garfont Village.
 * Zeke and Pandoria hide from the party as they leave Garfont Village.
 * Zeke uses Ultimate Lightning Fury Slash in Uraya.
 * Pyra confronts Malos in the Olethro Ruins.
 * Rex and Mòrag discuss their findings regarding Lila in Alba Cavanich.
 * Zeke uses Ultimate Lightning Fury Slash Max in Mor Ardain.
 * Bana appears in the Abandoned Factory after the party defeats Muimui's Tirkin guards.
 * Patroka and Mikhail confront the party in the Abandoned Factory.
 * Jin takes control of Aeshma in Temperantia.
 * The party runs past the box containing Giga Rosa in the Ardainian Battleship in Indol.
 * Giga Rosa appears before attacking the party in the Ardainian Battleship.
 * Akhos, Patroka and Mikhail confront the party at Genbu Crown.
 * Malos confronts the party in Balqors Ruins.
 * Amalthus speaks to the party using a hologram at the World Tree.

It also plays in the following cutscenes in Xenoblade Chronicles 2: Torna ~ The Golden Country:
 * Lora and Jin notice Malos's destruction in Lasaria.
 * Malos confronts the party in Auresco.
 * Malos confronts the party at the Soaring Rostrum in Torna.
 * Gort as a Blade Eater confronts Lora and Jin in Spessia.