Warmth

 is Disc 2, Track 3 on the Xenosaga Original Soundtrack and Disc 1, Track 8 on the album. ('Warmth' is an unofficial translation, as seen in the VGMdb listing of the album.)

It plays in the following cutscenes:
 * chaos has a one-way conversation with KOS-MOS as she sleeps aboard the Elsa.
 * The party reunites in front of the Old Church during the dive into KOS-MOS' subconscious domain.
 * MOMO gives Jr. the go-ahead to destroy the Song of Nephilim.