Z37b20a13t01t08le

z37b20a13t01t08le (called on the JASRAC database) is Disc 2, Track 9 on the XenobladeX Original Soundtrack. It is split into two parts: the first plays from the start until 0:28, and the second plays from then until the end.

The first part plays in regular battles when an enemy initiates the battle. Uniquely among the battle themes in the game, it does not loop; once it is through the regular battle theme (Black tar part 1 or 2, The key we've lost part 2, or z29ba2t0t1l301e17 depending upon the situation) begins playing.

The second part plays in the following story-required battles: The track plays in the following battles in non-story-required Affinity Missions: The track also plays as a boss theme in most Normal Missions (and often in the prior cutscenes if one exists), including but not limited to the following:
 * The Elder and Callow Grexs in the.
 * Glennar and the Prone Ruffians in.
 * The Brume Auravis during Renewed Will.
 * The Chief Qmoeva and Platoon Qmoveas in.
 * The Fierce Vigent during A Friend In Need.
 * The Tainted Sphinx in.
 * Ga Jiarg, Ga Buidhe and the Wrothian Warriors (on foot) in.
 * The Marnuck Soldiers and Marnuck Commander during Manhunt.
 * The Prog Ares in (for the first phase of the battle).
 * The Soldier Chimeras in.
 * The Dimnet Xiphias during New in New LA.
 * The Stratospheric Balaena during Fitting In.
 * The Stout Caro during Soldier of the Harriers.
 * The Gleaming Sphinxes during Then and Now.
 * The Agile Caecus during BFFs.
 * Gi Zang during The Gauntlet.
 * The Rexoskell during Definian Downfall (when it is fought in the Ganglion Antropolis).
 * The Sazon Caladar during Leaving the Nest.
 * Gadd and his goons during Professorial.

Etymology
The track title can be split into 3 parts: the prefix 'z37', the digits '20130108', and the letters 'battle'. The significance of the letters is obvious; the digits can be interpreted as the date 2013/01/08, or the 8th of January 2013, 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. 'z37' is a holdover from this codename.

Therefore, 'z37b20a13t01t08le' decodes into 'The 37th track composed for Xenoblade X, battle theme, recorded/mixed on the 8th of January 2013'.