(last updated: 12/28/17)A lot of people bandy about terms such as "Heaven" or "Hell" in the world. They use these words quickly, often without thinking at all about what they might mean. The truth is, the concept of an afterlife is something that becomes ingrained in an individual, and there are roughly as many ideas about what the afterlife looks like as there are people living in the world.
Strictly speaking, there are no rough analogues of these places in the world; no seperate dimension where consigned souls live. When a person dies, their energy returns to the world, in the form of the flowers blooming, and the grass growing. However, over the 200,000 years that human beings have lived on this earth, many have become too powerful for the world to hold in such mundanity.
People were more often born to war, strife and tyranny in ancient times, and in so doing, became more powerful than most of the complacent, enlightened people who inhabit what is called the 'civilized world' today, where the martial arts are most often practiced for sport instead of neccessity. As a result, a great volume of energy from exceptional warlords, dictators, masters and warriors came to occupy the flesh of the Earth. Over time, this energy--mostly chi--came to conform to stranded pathways winding throughout the natural system of things. These strands came to be known as 'leylines,' and they are the roughest analogue of the afterlife that anyone can know.
The leylines are inhabited by the collective essences of anyone who has ever become strong in their life. The energy, or 'spirit' of most people in the leylines--those whose strength would be considered comensurate to a normal sport fighter--lose all sense of selves in the great river of spirits, roughly the same as if a teardrop fell into the ocean. However, the memories and beliefs of a person are not so easily lost.
Certain concepts are universal to humanity--the ideas of Heaven and Hell, for example. Just as people tend to cluster by their social group in real life, so too do the memories of souls, gathering in one place or another based on their ideas. As a result, metanatural areas such as the Christian concept of Heaven or the Shinto concept of the Yomi are less 'physical places' moreover as they are cultural memes carried into the leylines by humans.
While on occasion certain phenomena and disasters can break the spiritual seal surrounding a leyline and transmogrify a physical area according to the spiritual polarity of that leyline's energy, most experiences relating to the afterlife have to do with people's chi entering the leylines and coming out with an impression of that energy. Certain spiritually-awakened people can 'experience' Hell by dying briefly, in this way.
For souls (and certain individuals with sufficient power), the experiences created by these leylines are of absolutely real spaces, with distinct physical locations. At what point does fantasy become reality? One could say that the leylines are, to that respect, a seperate world of their own.
While it has relative little bearing on today's society, most of the spirits in the leylines are insensate or trapped in certain locations which may or may not coincide with a physical 'space' in the normal world. However, certain spirits of powerful humans can wander all or part of the leylines pretty much at will, influencing lesser spirits and even interacting with other similarly powerful spirits within it.