Sora

 Sora is taken from the end of Chain of Memories, which means his Memories are not only unlinked from Namine fixing them, but some have strayed to Roxas and Xion and aren't even a part of him any longer. This makes fixing his Memories all the more hard when he leaves his own world for the DR. People and places may seem unfamiliar, or as if he should recognize them from memories of other people or places. 

As such he's very easily disoriented and forgetful. He may forget meeting someone new from one day to the next, or feel as if he should remember someone. This confusion is compounded when so many people look like each other in the DR.