The God of Decay is the twin sister of the God of Birth. They both created the means by which creatures would bear young. Her sister was responsible for Internal Gestation (carrying your young) while Breith-Dorcha created Larval birth and the idea of young that started as grubs, outside the mother. When the ancient “Ephemeral Promise” cast darkness upon the world, she chose to embrace it, effectively splitting from her sister.
Her realm, once inhabited by The God of Shadows with its great walls of stone, carries an atmosphere which is thick with a particulate made of the spores of all the resident growth. A symbol of the decay she spreads as she takes over its now ruined structures.