Chayah and Yechidah, the two highest levels of the soul, are treated differently in Jewish mourning custom than the three lower levels: because they are held to be rarely fully manifest even in life, sources speak far less about their state or destination after death than about Nefesh, Ruach and Neshamah, whose graduated departure shapes the structure of the mourning period itself. Where mourning practice offers specific acts said to elevate Nefesh, Ruach or Neshamah, comparable practices tied to Chayah are largely absent from the classical mourning literature.
This relative silence follows from Chayah's place in the doctrine's own history: the fivefold soul scheme, with Chayah and Yechidah added above the three older levels, developed later than the biblical and early rabbinic vocabulary behind Nefesh, Ruach and Neshamah, and mourning custom crystallised largely around the earlier, more established three.
Later Kabbalistic and Hasidic writing does treat Chayah as significant in its own right, corresponding in the widely used correspondence scheme to the fourth of the Four Worlds and associated with the living, willing aspect of the soul closest to its source, even where practical mourning custom has comparatively little to say about it directly.