Light creatures and death (How spirits are made)
ID: A diagram showing how petrified light creatures can more or less die normally, while the petrified bodies of ancestors prevents their light from leaving their body.
As light creatures age, the bond between their body and their inner light gradually weakens. Once the body expires, the bond is severed. The body returns to the earth, while the inner light returns to a place called "orbit". This is how things went before the construction of the crystal in Eden.
Following the crystal's fracturing, petrification took out much of the Kingdom's population, Spirits and light creature alike.
For other light creatures, death by petrification isn't so different from normal death since their light can still escape their body. The ancestors on the other hand were different. Because their light is located on the inside, their petrified body serves as a shell from which their inner light can't escape.
The bond between an ancestor's body and its light severs the moment the body is petrified, but over long periods of time, the light "forgets" there even was a body in the first place. When inner light is finally freed from its petrified body, the idea of "light" and "flesh" will have merged to become one, creating the ghostly appearance spirits are best known for.
In this state, an ancestor's (now a spirit) body *is* their light. Physical interaction with objects and others takes conscious effort due to their bodies being partly incorporeal. Spirits are also quite fragile compared to their former selves. With light-based bodies, things like dark rain or dark creatures can be extra dangerous.
ID: An ancestor before and after being petrified and subsequently being turned into a spirit. With their body serving as a barrier, environmental threats like dark rain aren't as dangerous. Being without their body, spirits are naturally more fragile.
Because they no longer have "flesh" to maintain, spirits are also functionally immortal. Keeping their light alive is the only condition for maintaining their existence. Spirits also do not age and their appearance reflects what they looked like at the time of petrification.