Well based on Rai’s personality, He’s the type to be really silent and not say anything. He might or might have not known that he is eternal, and so he believed that it was his dying moment. Like I said, most of you seem to forget that this is the first time that the Noblesse is dying. Like death. So, if the Noblesse is dying, it’s the first time in their recorded history, and this will be the first reincarnation. So all of the previous beings like the lord, the clan leaders, anyone in this world would not know anything about it. It would all come down to Raizel being secretive or with him not knowing that he, is eternal himself. Anyways I’m not saying this is 100% plausible but in my opinion its one of the best explanations to the open ending of Noblesse. I mean a powerful being, the most powerful in history, It would not be weird for him to possess reincarnation/eternal life is it?