Where We Used To Be

Where We Used To Be is Disc 2, Track 4 on the Xenoblade2 Original Soundtrack. It plays on the title screen of the main game of Xenoblade Chronicles 2, as well as in the following cutscenes:
 * Nia and Rex meet one another on the Monoceros.
 * Rex convinces Nia to stay with the party after her rescue in Gormott.
 * Vandham explains the death and rebirth of Blades after the party kills the Elder Arachno.
 * Cole reveals himself as a Flesh Eater.
 * Rex tells his dead parents about Pyra.
 * Zeke asks Rex about his Aegis-related preferences, and explains a bit about his past.

It also plays in Xenoblade Chronicles 2: Torna ~ The Golden Country, in the cutscene where Addam and Lora discuss their Blades on the Ardainian battleship.