|SPOILER WARNING!! Spoiler warning! This article contains information from recent released episode(s) and/or chapter(s). It may contain SPOILERS.You are warned about it, okay?|
Both versions of Kamui have a tendency towards violent reactions, of course referring particularly to the Kamui of the earlier X volumes. In the first volume of X, Kamui requires very little provocation from Daisuke before he begins attacking him with lethal intensity. Vampire Kamui, when facing the Tsubasa travelers for the first time, shoots first and asks questions never. Had the travelers been less skilled in fighting, they might not have survived the encounter and their death would most likely have not troubled Vampire Kamui in the least. There is a difference in their sense of violence, because Kamui generally fights with a fiery intensity that is intrinsically emotional, whereas Vampire Kamui usually fights with cold, but frighteningly deadly, skill. The only time he reacts more like Kamui is when Seishirou's name is brought up. In that case, he does lash out emotionally and is easily overcome. In X, Kamui's tendency towards violence could be attributed to reacting out of fear and pain, rather than a natural part of his personality, since he quickly becomes less violently inclined once be begins to trust his new companions. The source of Vampire Kamui's violence is less clear. It could be simply a part of his vampire nature or a result of his lifestyle. Certainly his more emotional response to Seishirou is likely a matter of specific anger and fear, either of the man himself or what he plans to do.
Another characteristic both version share is a general lack of attachment to other people; however, when they are attached to someone, they form powerful bonds. As something of a social outcast, Kamui possesses very few relationships, which makes his friendships with Fuuma and Kotori even more meaningful to him. He would endure any hardship in order to keep them safe and happy. Overtime he also develops bounds with his fellow Dragons of Heaven, though their intensity never quite reaches that of his connection with Fuuma. Vampire Kamui, on the other hand, has only one attachment that seems to hold value to him, and that is his brother Subaru. Even though he spent at least two years with the Tower Group, they still apparently mean very little to him, especially in comparison to Subaru. When Subaru revives, he wants to leave as quickly as possible, even though the Tower Group is currently experiencing a major crisis. For Subaru, however, he would endure anything, even two years of loneliness to ensure his brother's safety. Again, Kamui suffers from a sense of isolation, so attachment and trust would be a difficult matter for him. Once a bound was created, it seems reasonable to an otherwise lonely person to protect and cherish that relationship under any circumstances. Vampire Kamui remains a bit of a mystery. Perhaps, like his counterpart, he has had little opportunity in the past to form attachments beyond that with his companion. If that is the case, it would make sense if his intense hostility towards Seishirou is as much a matter of jealousy and fear of abandonment as actual fear of harm towards himself and his brother. Of course, this is all speculation since the details of his conflict with Seishirou remain unexplored in the text.
Another characteristic the two versions of Kamui share is distaste for losing. Kamui of the first few volumes of X not only nearly kills Daisuke in the first volume, but considers fighting Arashi in a later volume because she had the nerve to take his "prey" away. Not only does he want to win, he wants to annihilate his victim. In later volumes, winning also becomes an issue, this time because of the guilt he feels when others suffer because of his perceived inadequacies. Vampire Kamui also insists on not losing, even if the matter at stake is something he claims not to care about. The Fuuma in Acid Tokyo uses this to manipulate him into doing something he did not want to do--sit down and talk with him about the future of the reservoir--simply by suggesting that failing to do so would imply losing.
Both versions of Kamui initially seem to be very selfish, uncaring individuals--Kamui says as much in his battle with Daisuke. X quickly reveals this to be a scam, an illusion to keep people away from him. He may lack a pervasive sense of altruism, but that does not mean that he does not care about others. In fact, Kamui actually seems like a rather kind, young man who really does want others to be happy. He may not understand people very well, but he does try to do what he thinks is best for those around him. His decision to try and stay away from Kotori and Fuuma hurts them, but it was from a desire to keep them safe. When he initially refuses to eat with the others following Daisuke's death, he does so because he fears his presence will make his companions uncomfortable. He does not understand that his absence troubles them terribly because he does not seem to know how much they really care about him. Vampire Kamui, however, seems far less compassionate in general. Although he protects the reservoir, which helps the Government Building people considerably, he does so entirely for his own purposes--their plight barely seems to register for him. He gives Fai his life saving blood, but not out of compassion for the Tsubasa group, but out of concern for Vampire Subaru and their safety. Even Fuuma of Acid Tokyo seems to have more compassion than Vampire Kamui, especially towards Sakura as she prepares to travel out into the city at night. Still, his actions are of aid to others and, while his intentions might not have been born of compassion, have value to those he helps. The Government Building people certainly acknowledge his role in their survival and Mokona, in particular, thanks him for saving Fai. Of course there is also the concern he shows Vampire Subaru. His well being might be the one thing Vampire Kamui cares about more than anything in the multiple dimensions. Perhaps if his circumstances had been different, Vampire Kamui might have become more compassionate like his X counterpart.
The area in which Kamui, particularly that Kamui of the later volumes, seems most different from his vampire counterpart is confidence. Kamui seems incredibly unsure of himself for most of the story, despite his attempts to appear otherwise. He worries about his inability to protect others or discover his true wish. His actions, such as they are, tend to be indecisive largely because he is unsure if he is right. Although as Kamui he is the most important member of the Dragons of Heaven, being the one who can wield the Holy Sword on the final day, Sorata is actually the leader of the group since he is the one who makes decisions and directs the other members. Still, one could argue that the Kamui of the earlier volumes seems confident enough, but, like his violence, this could simply be a smoke screen for his insecurity. It is hopeful that the discovery of his true wish will allow Kamui to obtain a level of true confidence which will enable him to end the conflict once and for all. This remains to be seen. Vampire Kamui, on the other hand lacks any sense of indecisiveness. He acts with absolute confidence in his decisions and his abilities. To regret, it would seem, would be to admit defeat. When Fuuma mentions Seishirou's intention to find Subaru again, Kamui darkly replies that he will never allow that to happen again. He is confident that he has the strength to protect his brother, yet the fact that they are on the run and that Kamui is particularly anxious to keep moving belies his confidence. He may not be as indecisive as his alternate version, but Seishirou does appear to frighten him quite badly.
Their relationships are really the main difference between the two characters. Kamui was raised in relative isolation except for those few happy years with Kotori and Fuuma. The one person he thought he could always count on betrays him in the most vile and heartbreaking way imaginable. Still, he is able to make connections with other people who care about him and who he cares about in return. Vampire Kamui, however, has a powerful relationship with his brother which is his apparent lifeline. While Vampire Subaru is unlikely to betray him in the way Fuuma betrayed Kamui, Vampire Kamui still seems rather desperate to maintain their connection. On the other hand, he seeks out no other connections, even with the people he leads. He remains a shadowy presence, protective yet distant. He may do so out of necessity--emotional attachments might make constantly moving around difficult--but that is pure speculation. Nothing in the text suggests a deeper need for connections for Vampire Kamui, unlike the Kamui of X.
So what of CLAMP's statement--is Kamui really the same no matter which dimension he is in? It's a little hard to answer. Kamui's story remains unresolved and Vampire Kamui's remains vague. One could certainly make a case that they are very different, but one could also make the case that they pretty similar, but that their circumstances make them appear different. It really depends on what one wants to read into the text.