Battling KOS-MOS

 is Disc 1, Track 10 on the Xenosaga Original Soundtrack and Disc 2, Track 8 on the album. ('Battling KOS-MOS' is an unofficial translation, as seen in the VGMdb listing of the album.)

It plays in the following cutscenes:
 * KOS-MOS saves Shion from a Gnosis on the Woglinde.
 * KOS-MOS shoots at a Gnosis while the Zohar Emulator is taken from the Woglinde.