Of souls, sentience and afterlife

What divides sentient and sapient beings from mere animals (and from daemons) is existence of souls. What exactly are souls, and how do they work?

Souls

Each and every being has a certain level of connection with the Dark, the more developed being the stronger this connection. Mortals, for example humans, have stronger link with the Dark, which is a world of thoughts, memories, and abstract thoughts than dogs or other animals, does their capacity for them is much greater.
What is really important is development of brain (or other neural tissue responsible for making decisions, since for example plants are included too), which serves as transmitter permanently connected with that concrete being's soul. Brain is, in fact, responsible mainly for this connection, overseeing only those actions that do not require human active thinking (for example, heart beating). The rest is done by human ego, which resides in soul within the Dark, with all emotions caused by interference with thoughts and emotions that the Dark is made from.
Soul can be described as a immaterial shell that covers ego – and memories, that are stored there and accessed via link with the brain – that remains in the Dark, creating minds as we know them. Exact details are next to unknown, as any sort of interference with soul is banned by every single religions worldwide, with most of them considering it worse possible taboo. For souls are a realm over which divines rule, with every single attempt to change it ending with terrifying disasters mainly due to mortals imperfection that together with delicate nature of soul tends to cause terrible consequences.
Souls carry ego, that oversees actions done partially willingly and partially automatically by the body. They are created at the moment of conception, as nothing more than a minuscule seed that won't grow into true soul until the brain will start working. From that moment onward the soul is practically eternal, as death of the body can't influence it in any meaningful way – if it happens earlier, the unfinished souls dissapear into nothingness. Soul – and the mortal body that is governed by its internal mind – begins its existence, and exist through sort of a tutorial that is mortal life.

Afterlife

What begins as one out of millions similar souls slowly grews into existence unique on the scale of multiverse. It grows, learns about the world, becomes unique in its experiences, worldview or simply existence... and then, finally, death cames. Death that is a moment of dread for mortals, while nothing but a minuscule transformation for the divines. As the body dies, the unique soul severs its connection to it, and continues unto an afterlife in the Dark, guided there by various gods and daemons tasked with this arduous task. With every god having his own personal preference in terms of those, whom he wants to let spent their eternity in his domain. In most cases taking form of list of various sins and virtues imposed on their followers.
Afterlifes vary greatly. Some are a perfect, unending versions of Real Worl, without hunger (but where one can eat for pleasure) or pain. Others are undefined place of happiness, where souls bask in the light of their god, feeling nothing but an eternal happiness and internal peace. Others are places of fire and pain, when those that lead sinful life are receiving their penance. All of they are no longer on Material World, and all of them filled with people who remember every single detail of the life, even those that they forgot before death due to imperfections of their bodies... unless they live in a good place and have their painful memories washed away according to their will. With those living in recreations of Real World being a sort of exception, since they tend to periodically forget any new knowledge, so that they can never get bored, discovering the same things over and over again, remembering permanently only things they decide to remember.
Not only mortals are subjected to afterlife, this includes also animals (in most cases those that were close with mortals and are 'afterlifed' by association, mainly various pets), and, rarely, certain daemons that were so close to certain mortal (mostly due to romantic relationships some of daemons are capable of) that they decided to follow them into afterlife.
The situation of atheists is much more grim, since there is no god willing to take them, unless (which is one of the few exception) to their versions of Hell, which is however rare. The rest remains abandoned in the Dark until it slowly dissolves, leading to the cessation of existence. Other possible endings include being reincarnated (there are some deities that allow something like this, but with the soul made blank slate beforehand), or becoming a toy for some daemon, in most cases evil and devious since only such beings are interested in such souls.