Z12e201v2e091n4t

z12e201v2e091n4t (called on the JASRAC database) is Disc 2, Track 11 on the XenobladeX Original Soundtrack. It is split into three parts: the first plays from the start until 2:00, the second plays from 2:00 until 4:37, and the third plays from 4:37 until the end.

The first part plays in (most) Ganglion bases: It also plays in the following cutscenes:
 * The Bedrock Hold in Primordia.
 * The Seaswept Base in Primordia.
 * The Ensconced Citadel in Noctilum.
 * The Lakeview Stronghold in Noctilum.
 * The Jair Fortress in Oblivia.
 * The Mesa Fortress in Oblivia.
 * The Milligan Supply Base in Oblivia.
 * The Scabland Fortress in Oblivia.
 * The Badr Stronghold in Sylvalum.
 * The Hilal Stronghold in Sylvalum.
 * The Boxtrap Checkpoint in Cauldros.
 * The Ganglion Antropolis in Cauldros.
 * The Kitsune Stronghold in Cauldros.

Main story

 * The party notices signs of a battle across Oblivia in.
 * Doug requests that the party take care of his last data point during Close Comrades.
 * Elma briefs the party on their duty for the Ganglion invasion in.
 * Gwin tells Mathias where Aisha was last seen during Nine Lives.
 * calls Elma and her team over to the Hangar in.
 * The party reaches the point of no return in.

Sidequests

 * The party finds Gerome in peril during Murder Most Foul.
 * Tika finds out why the Sparkjet Rifle exploded during What the Skell?!.
 * Phog approaches the five Oc-Serv Yabar during A Great Divide.
 * Frye learns that Phog is in danger during Blitzkrieg (if the player chooses to go to Bedrock Hold with Frye).
 * The party finds the 'wounded' Lara Nara during Climbing the Ladder.
 * The real Hope confronts the fake Hope during A False Hope.
 * Nagi insists upon carrying Orton back to NLA during Reporting for Duty.
 * Tatsu sees a Bizarre Insidia running away with his father's glasses during The Ties that Bind.
 * The party confronts Malyteth for the second time during The Miracle Maker.
 * Staccata claims that Fraisie's 'miracle water' is an antitoxin during the same mission.
 * The party finds Clemons's body during Attack on Biahno Hills.
 * DE913: Dieara shoots HT665: Erio during the same mission.
 * Loda Gorida confronts the lovers during Forbidden Love (if the player doubted that Leroy could take care of Lavina Couba).
 * Gadd and his goons confront Professor B during Professor B.'s Return.
 * The Miramobile overheats and goes critical during the same mission.
 * Zo Ozuchi reveals that he is the party's final opponent during The Gauntlet.

The second part plays in certain (often hidden) areas around Mira: It also plays in the following cutscenes:
 * The Silent Mire in Primordia.
 * Unicorn Rock in Primordia.
 * Dead Man's Gulch and Millstone Ridge in Noctilum.
 * The Weeping Whitewood in Noctilum.
 * Central Ibra Ravine in Oblivia.
 * The Floating Reef in Oblivia.
 * The patch of sand 1 hex southeast of FN Site 305 in Oblivia.
 * The Abyss Reservoir in Sylvalum.
 * The in Sylvalum.
 * The Noctilucent Sphere Interior in Sylvalum.
 * The centre of western Lake Ciel in Sylvalum, 1 hex southwest of FN Site 408.
 * The M'gando Volcanic Crater in Cauldros.
 * The O'rrh Sim Castle Ruins, O'rrh Sim Gate, O'rrh Sim Keep, and the Ganglion Weapons Hangar in Cauldros.
 * Slavebird Isle in Cauldros.
 * The White Phosphor Lake in Cauldros.

Main Story

 * Elma consults with Lao regarding information about the Lifehold signal before the party heads off to Noctilum in.
 * L is introduced to in Chapter 4.
 * Elma offers to escort Lao's teammates during A Friend In Need.
 * The party first brush with the Tainted Caro in.
 * Lin performs the analysis of the last data point during Close Comrades.
 * Elma realises that the party had fallen for a diversion in.
 * Nagi talks with the party before they head off on their mission during Spy Games.

Sidequests

 * The party views the security camera footage during Lakeside Getaway.
 * The party finds Camber after the weapon test goes awry during Rapid Misfire.
 * The party finds one of Solan's escorts during A New Rival?.
 * Ada and Hope hatch a plan to bring out the latter's doppelgänger during A False Hope.
 * The party learns that Leland Cole is alone during Fathers and Sons.
 * Alan discusses the difficulties of increasing the beam cannon's power output by 800GW with Lin during Two Peas in a Pod.
 * Murderess betrays the party during My Dream.
 * Murderess learns about Yolanda's betting game during The Little Rich Girl.
 * Murderess deduces with Eleonora that the murderer of Otis and others may be her parents' killer during Serial Thriller.
 * The party finds Tatsu's departure letter during To Serve Nopon.
 * Yelv presents the party with missions at the start of Meeting Yelv.
 * The party reports back to Yelv once said jobs are completed in the same mission.
 * Yelv asks Eleonora if she can locate the rest of his partner's body during Yelv's Partner.
 * The Blood Lobster communicates with Cross after they find the 49th stuffed lobster during Rise of the Blood Lobster.

The third part plays in the following cutscenes:
 * The Vita is airlifted out of Noctilum in Chapter 6.
 * Ryyz takes control of the Zu Pharg in.
 * Mathias grabs Aisha from in front of the Greedy Forfex during Nine Lives.
 * Luxaar appears with the Vita inside the Lifehold Core in Chapter 12.
 * Gadd and his goons confront Professor B during Professorial.
 * The Blood Lobster communicates with Cross after they find the 98th stuffed lobster during Rise of the Blood Lobster.

Both the first and the second part are one of few area themes that take priority over Don't worry.

Etymology
The track title can be split into 3 parts: the prefix 'z12', the digits '20120914', and the letters 'event'. The digits can be interpreted as the date 2012/09/14, or the 14th of September 2012, the date in which the track was recorded or mixed.

The track is one of several in the XenobladeX Original Soundtrack beginning with 'z' and a number (possibly followed by 'b'). The significance of this is that the composer Hiroyuki Sawano gives codenames to tracks before he properly titles them: a letter/abbreviation followed by a number, where the letter/abbreviation corresponds to the soundtrack in question. In the case of Xenoblade Chronicles X, this letter was 'z' (Xenoblade X's Japanese name, ゼノブレイドクロス, can be romanised as Zenobureido Kurosu). The number corresponds to the ordering in which tracks were composed. 'z12' is a holdover from this codename.

Therefore, 'z12e201v2e091n4t' decodes into 'The 12th track composed for Xenoblade X, event theme, recorded/mixed on the 14th of September 2012'.