I think the "chasers" are a new being like the Heartless or Nobodies
When someone becomes a Heartless the soul and body become the nobody
but what happens to the memories? Thats what I beleive creates the "chasers"
the heartless and nobodies don't keep their memories so they must go somewhere.
The line in the KH2:sm "memory of Xehanort" may be refering to the ES, since he looks like xehanort and may be his memory, also the BHS may look like roxas because he could be the memory of sora, yes i know sora has his memories, but he lost them while he was a heartless, so there could be two of his memory, one that returned to him and one that became the "chaser". As for the blue haired girl I have no ideas, she may be the memory of kairi but most likely not since kairi didn't have a heartless, just a false nobody.
