Where We Used To Be

Where We Used To Be is Disc 2, Track 4 on the Xenoblade2 Original Soundtrack. It is an arrangement of Elysium, in the Blue Sky for solo piano. It plays on the title screen 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.