X-BT2

X-BT2 is Disc 4, Track 5 on the XenobladeX Original Soundtrack. It is a version of Wir fliegen with the vocals replaced by a synthesiser.

It plays when Professor B uses his Miramobile to travel back to the future in Mystery Man, and also when he uses it to return to NLA during both Professor B's Return and Professorial.

Etymology
The track's title is most likely an acronym for '(Xenoblade Chronicles) X - Bonus Track 2'.