Loneliness

Loneliness is Disc 4, Track 13 on the Xenoblade2 Original Soundtrack. It plays in the following cutscenes of the main game of Xenoblade Chronicles 2:
 * Azurda's giant form is destroyed after taking heavy damage, leaving behind his larval form.
 * Nia talks with Vandham about her history in Torna.
 * Rex talks with Pyra about her hidden power after Vandham's funeral.
 * Muimui tells the party that Soosoo was killed and that he does not know of Tatazo's whereabouts.
 * Fan la Norne, Rex and Nia talk about Fan's missing memories.
 * Nia, Brighid and Poppi each attempt to get Rex not to give up in their own ways.
 * Malos steals Pyra's memories at the Cliffs of Morytha.
 * Nia's cell-replicating attack incapacitates Malos at the Balqors Ruins.
 * Jin tells Brighid that she's "exactly like (she) used to be".
 * Zeke and Amalthus discuss life and killing in Indol (flashback).
 * Rex breaks down over the illusory dinner with Pyra and Mythra.

It also plays in the following cutscenes in Xenoblade Chronicles 2: Torna ~ The Golden Country:
 * Lora recalls Jin's first words to her upon his awakening.
 * Addam suggests that Lora, Jin and Haze join his fight against Malos, and talks to Mythra about the differences between her and ordinary Blades.
 * Lora pays her respects to her deceased mother after the fight with Gort.
 * Minoth considers Mythra and Malos after joining the party.
 * Lora and Milton talk about their past in Hyber Village.
 * Azurda and Jin talk about their fates in the Tornan Titan's matrix.