darkness of the heart; hidden depths of the mind
Refers to the hidden, often negative or troubled aspects of a person's psyche; used in psychological, literary, or dramatic contexts.
It is said that the darkness in his heart lies behind that incident.
parental anguish over a beloved child
Archaic sense; historically used to describe a parent's deep worry or distress about their child, often in classical or literary works.
In classical literature, 心の闇 can express a parent's anguish over their child.