RaTEoREkiSImeAra

raTEoREkiSImeAra (called on the JASRAC database) is Disc 3, Track 13 on the XenobladeX Original Soundtrack. It is split into two parts: the first plays from the start until 3:55, and the second plays from then until the end.

The first part plays as the battle music for the Vita in, as well as the cutscenes immediately before and between the two phases of the boss.

The second part plays as the battle music for Telethia, the Endbringer. It also plays when Telethia swoops down and easily does away with the Tainted Sphinx in.

Etymology
Separating out the lowercase letters from the uppercase in the title gives 'raokimera' and 'TERESIA' (which aligns with the JASRAC version of the title). These are alternate romanisations for 'Lao chimera' and 'Telethia'. The latter refers to Telethia, the Endbringer; the former likely refers to Lao's transformation as a chimera, although it is unclear what this track has to do with that.