Z5m20i12r04a28

z5m20i12r04a28 (called on the JASRAC database) is Disc 2, Track 2 on the XenobladeX Original Soundtrack and Track 5 on the Xenoblade Chronicles X Soundtrack Selection. It is split into two parts: the first plays from the start until 2:42, and the second plays from then until the end. The first part is a remix of N木ig木ht木L.

The first part plays in the cutscene when the sky clears as Cross sees the expanse of Primordia for the first time. The second part plays in the following cutscenes:
 * gives the order to attack the Ganglion in.
 * The party catches a breather between waves while defending the East Gate in Chapter 8.
 * The party encounters the attacking Ajoa during Lakeside Getaway.
 * The Falconine Jacul 'saves' Mia from falling during Mighty Mia.
 * De Soghu arrives and berates De Ezich during Leaving the Nest.
 * Tolba Wolfen asks the party to defeat several Tectonic Puges during The Duel (Part IV).

The vocals from 1:52 were sung by Mika Kobayashi; the other vocal parts were sampled from Apple Loops.

Etymology
The track title can be split into 3 parts: the prefix 'z5', the digits '20120428', and the letters 'mira'. The significance of the letters is obvious; the digits can be interpreted as the date 2012/04/28, or the 28th of April 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. 'z5' is a holdover from this codename.

Therefore, 'z5m20i12r04a28' decodes into 'The 5th track composed for Xenoblade X, Mira's theme, recorded/mixed on the 28th of April 2012'.