The Middle Level was the second realm to come into existence. It is notably the home of the Reapers and the Silenhetta. The Middle Level is the most inhabited realm. Many souls are processed in Keski and then it is decided if they should be sent back to the Upper Level or to do the Lower Level.
The face of the Middle Level is the goddess Paradigm. Resisting Paradigm while living in the Middle Level can lead to the resisters being institutionalized and reprogrammed. This is necessary as resisting Paradigm can lead to an outbreak of discord. Many people deal with Paradigm's existence by choosing to worship her. She is the least understood thing in this universe, and souls love to worship things they do not understand.
Souls that live in the Middle Level have the largest understanding of the universe as most souls that lives there has experienced death at least once. Memories of souls' past lives often linger in this realm. Institulization is common among new souls in the Middle Realm as they tackle the fact that they have experienced death and have lost the things of their past life.
The Middle Level is the most connected realm to the Void which results in the Void leaking into parts of the Middle Level at times. Many souls go missing as a result of this leakage.