Rem is the aggregate sentience of the sixth fonon - in other words, the light element.

Lorelei, from what I've managed to piece together, is the hypothetical aggregate sentience of the seventh fonon, although the seventh fonon itself is difficult to classify. Some call it the fonon of sound, while others associate it with memory, because it's necessary to read the Score, and life, because it's the fonon used in most healing artes.