The Reader is the unnamed player character of Pyre. A Reader also generally refers to anyone who can read the Book of Rites.
You were sentenced to the Downside for the crime of literacy, as the use of literature nearly resulted in a cultural insurrection in the Commonwealth. You are physically incapable of participating the Rites due to being heavily crippled before the story even begins; however, as the only literate one, you were rescued by Hedwyn and brought into the Blackwagon to become their Reader for the Rites.
Your gender and background depends on the options you choose within the game. Your can be a crippled scholar, farmer, or war orphan. You may also choose to keep silent about your past, leaving you with no history.
The Reader is the Nightwings' guide during the Rites. You direct them in the Rites, and consult the stars to guide them from Rite to Rite. You help the Nightwings through the course of the Rites and in their personal lives, offering counsel on which road to take and advice in the back of the Blackwagon when someone has something on their mind. While you don't take part directly in the Rites, the Nightwings respect you as a Reader and as the de-facto leader of the Nightwings. They let you decide who should be liberated at each Liberation Rite.
Through reading the Book of Rites, Readers gain the ability to read thoughts and communicate mentally with others. You use this ability to learn the Moontouched Girl's name, and to communicate with Ti'zo. Readers also gain mental powers such as memory alteration and mind control. The Archjustice communicating with you in your dreams may be an extension of his abilities as a Reader.
The Book of Rites holds that only a Reader may become the Voice to guide the next generation of exiles. Due to the fact that the Rites end during your lifetime, this path was only for the current Voice, not for you. However, you can still earn your freedom in the final Liberation Rite. When the victor prepares to enter the stream back to the Commonwealth, the stream turns red, and the victor must choose someone to return. There is option for you to be chosen.