I think its guy trying to get through to Kakashi whilst he is in thought.
I also think Tobi is Obito. It makes sense. Their Kamui leads to the same dimension. Also, Tobi is missing the Sharingan from his left socket and kakashi has one in his. His memory is of the memorial where Kakashi would go to morn the loss of his two companions Obito and Rin. Also, Kakashi asked Tobi, in the previous chapter, where he acquired his Sharingan. He either knows its Obito at this time or he thinks someone stole the eye from Obito's "dead" body. This could mean that Tobi stole the eye because he acquired it at the battle of the Kannabi bridge or Tobi is Obito. Obito did gain his Sharingan during the battle for the kannabi bridge.