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 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.