It's been a long time since I read this manga.
But I recall some discussion and speculation that Swordfish Knight was Anima reincarnated.
I vaguely think I recall that Swordfish Knight was very knowledgeable and had been around for a while.
But is there any evidence that would cinch the possibility that Swordfish Knight was Anima reincarnated? To begin with my understanding of the reincarnation cycle is pretty non-existant.
Additional evidence for this appears to come from the ending of Spirit circle in a reference to an esper.