The Equivalent Phenomena

The Equivalent Phenomena is a prominent condition in Map of the Woods. It is the source of all Equivalents.
When a baby is born, it has a certain amount of magic energy stored in its body. A baby cannot contain it all, so its magic energy splits in two and forms a vessel item. The vessel item, though appearing inanimate at first, eventually develops into an equivalent child mirroring its human counterpart. The initial item forms the child's head. As the two grow older, they grow apart in physical form, to where adult equivalents are very distinguished from their equal.
Some important terminology:

• People are called 'equals' if they are each others' counterparts. Many also refer to their equals as siblings, such as brothers or sisters.
• As mentioned before, the vessel item is the item that the split magic energy manifests into. There is possibly genetic linkage in what the item is; for example, a parent with a plant-head equivalent may have a child with a plant-head equivalent as well.

And now, here are the Laws of Equivalents:

1. A human and their equivalent have something called an 'equal bond'. The duo's magic energy is stored between both bodies, creating this bond.
2. Equal bonds cannot be broken, with one exception:
3. The equal bond breaks when one of the equals dies. When one dies, their magic energy transmits to the other equal, causing them to die as well because their body cannot handle all the energy.

Causes

The original trigger for the Equivalent Phenomena is currently unknown; popular theories speculate it may be of divine origin or the result of magic culminating in humans over many years.
However, the Phenomena only takes place once a baby is born, and does not occur if the baby is stillborn. It does occur even if the baby dies of other causes, such as illness.

Sequela

In some cases, coupled with the overuse of magic abilities, Energy Sickness can occur in humans or equivalents. More information is available on its own page, but in short, the sickness makes it so one or both equals cannot contain their magic energy, becoming slowly drained over time. The result is always fatal, but the speed at which the process proceeds varies.

Affected Groups

All humans born after the Phenomena began are affected, with no exclusion.

History

Before the Phenomena's start, people knew very little about magic, especially as an energy. About 100 years ago, babies started being born with 'equivalents' appearing soon after birth--around this time, people slowly began to understand how to use symbols, and the idea of magic as a form of energy became more prevalent. 
Since having one baby meant having two by default, the world suffered from a population boom. Equivalents and newfound magic powers also lead to devastation in the form of high spreads of Energy Sickness and the use of symbols in combat or failed healing. In the modern day, many towns are much smaller than what they used to be due to this devastation. While not quite apocalyptic, the world is still trying to recover and reorganize itself.
The Magic System describes magic as an energy more in-depth.

Type

Magical

Children

• Energy Sickness

Origin

Magical

Cycle

Chronic, Congenital

Rarity

Common

Affected Species

• Equivalent
• Human