Well, heres my not very lengthy theory i just happened to think up. Unversed are dark thoughts made real. Nomura said that Unversed are related to bad thoughts. Maybe these negative thoughts collect and form a being that attacks people to collect their thoughts which are released when these Unversed defeat a person. The form of the created unversed could depend on what thoughts they were created out of. For example, violent thoughts lead to a violent Unbirth. These unversed also rely on their own anger and hatred to retain their own sense of existing, and just like nobodies, they do not really exist the "those that are not versed in life" supports this. Also like Nobodies, Unversed are destined to eventually fade back into darkness. Their purpose for collecting the thoughts are possible for a few things. 1. To remember their emotions and what things feel like. 2. To gain thoughts of a heart. Unversed also, like Heartless rely purely on instinct and do not think and plan like Nobodies. This theory is kind of a stretch, but who knows?
