Content warning: Suicidal ideation, child abuse, emotional abuse
I hc Seto Kaiba to have NPD comorbid BPD traits. He’s actually a pretty good example of someone who experienced C-PTSD in childhood and adjusted those traits of trauma and coping throughout the series in alignment with these cluster B personality disorders, and grew from it (considering that earlier in the series he has a mind crush that means that the Seto Kaiba he have now throughout the series is actually the best version of him we have).
This man has such a strong sense of seeing things 'good' or 'bad' (especially concerning dual monsters, a title and area of his identity that he holds very dearly) that he decides to blow up an entire island he made just because he lost a tournament to Yami Yugi. Each time he wins he feels on top of the world, each time he loses he has to do something (anything) to control his environment in an effort to reestablish his ego. For me, I interpret this as a sign of splitting.
Heck, I saw a comment that jokingly stated that he doesn't make efforts to socialize, he sets up tournaments to do that. The more I think about it, the more I feel that actually rings pretty true. His supply he seeks out from recognition, attention and respect from others in a large scale in general, so I think that is rather appropriate.
This ties into the complex but nuanced way he gradually establishes a complicated but closer connection to Yugi and his friends.
When Jonouchi (Joey) was in very critical condition and in a temporary coma due to a bunch of the participants (Yami Marik) rigging the card game tournament with dark magic to be capable of killing people, he refused to park the zeppelin for medical aid and was more annoyed that the Istars interfered with his tournament. He didn't even care that Jonouchi could have died.
He does not spare any remorse or sympathy for Noah, (his adopted step sibling from Gambino in season 4) in the anime when he knows he was used and abandoned by the same father figure they shared and just tries to push him aside to secure Mokuba and escape the virtual world. He literally has the perspective (especially post mind crush) that he is a very important person that takes himself seriously and that people who get hurt (and are not in a few particular range of people he knows and respects) are just not worth caring all that much.
This, and not ignoring the fact that he didn't really hesitate to show any remorse (pre-mind crush) about Yugi's grandpa getting to be hospitalized or that he literally made an entire amusement park to kill Yugi and his friends or even put a lowkey torture device on his brother (literally the only person he likes and enjoys being around) in the manga before the events in the anime series just tells me he has low empathy. He doesn't try to do this to be a sadistic person or a general asshole (the only instance where he is is comedical with Jonouchi concerning the dog jokes he jabs at him with or making snide comments to Zigfried or other things of that nature) but it mostly treating others in the cost by cost basis concerning his goals regardless of the stakes at hand until it is extremely personal to him.
When he is presented situations that where he would be unable to secure his brother due to Pegasus keeping him hostage if he doesn't succeed to the finals of the season 1 tournament, he doesn't even hesitate to goad and attempt to guilt trip Yami with suicidal ideation when he knows he will lose the duel otherwise. He stands on top of the edge of the castle they are dueling on states "Oh I might stumble from the tremble of your attack and die of the ledge of this area and die :(" to goad him to give up, regardless of what extreme it will take to secure his goal... He isn't even threating to end himself because he is suffering or that he generally is interested in doing so by any measure, it's a manipulation tactic that would ensure he could save his brother while not having to compromise and beg or even explain his situation to the others and not seem desperate to bother and ask for help.
Now, is this okay and justified? Obviously not. But it explains why he acts the way he does, especially the hyper-independence he displays from his childhood trauma and abuse he suffered from Gambino. Which, yes, that also explains a parallel in which he didn't feel remorse for Gambino (as horrible of a father figure as he was) ending himself by jumping out of a window due to Seto basically stealing his company from him as literal child to later mirror him as well. Treating his brother Mokuba badly (temporarily in the beginning) for failing him earlier in the manga with the electric zapping device, pushing others hard to the extremes to could kill them to the extent that he does (notably when his ego and reputation have been compromised) especially earlier in the series are just things he picked up and replicated from his childhood and the efforts he had to endure to survive in a environment that operated only with cold hard respect.
I don't believe he actually has no empathy though, he has strong cognitive empathy and the possible small amount of emotional empathy/sympathy for the situations he find himself in he fosters and gets better at as he exposes himself to Yugi's friends that (thankfully!!) do not foster extreme resentment for what he did to them and offers a relatively good amount of unconditional support to him regardless of his status of the king of games or his wealth.
He saves Anzu (Tea) from a life or death card duel where she was held hostage later in the series when this would have been unheard of for him earlier in the series. He provides a extensive amusement park for the younger children to experience duel monsters ( in modern graphics) in a healthier and safer environment than his generation had and enriched their childhoods alongside extending his brand and company. (Aka, things he never experience as a child concerning his love of games.) Yes, it is for profit and a part of his plan to establish his range of influence for his company, but I do believe he really does want to give others a better experience of things he wasn't afforded to as a kid, and did that through the very same Duel monsters he took over and improved over time.
He balances out his behavioral traits to be less self focused over time to help out Yugi, his friend, and by in large society with the technology the literal advancements technology that is unprecedented and advanced humankind in a large scale degree. I'm not kidding, check out the video below concerning his large scale breakthrough contributions he did to the field of physics and by extension the entirety of civilization in the process of fulfilling his personal and sometime absurd/petty goals.
And, he comes around to actually befriending and confiding in Yugi (and somewhat his group of friends) as his own person and especially as a duelist at the end of the Dark Dimensions movie with not only respect, but general companionship concerning the entire ordeal they went through concerning their mourning over Yami.
Also, I think it's appropriate to assume that Yami wasn't only Seto's rival at a certain point, but as his FP. The fact that in season 5 of the anime and by extension the Dark side dimension movie of how he was willing to witness the ceremonial duel and try to obsessively resurrect Yami tells me (other than the strong platonic or romantic infatuation he could harbor for him, take your pick) that he was the only person he could place his "favorite person" designation to out of anyone he has known before. He is the only person that Seto respects probably more than himself (than he would publicly care to admit), likely fell into somewhat of a depression when he was brought back into the afterlife and focuses his mourning by building stuff to meet him again, and in every instance Yami Yugi does not meet those expectations or is close to giving up in his duels due to terribly high stakes in the series Seto sets himself straight very crudely (in his own Seto way of expressing disappointment to encourage him ironically enough) in a way that seems like extremely strong personal inclination to do compared to the other characters.
I would hazard a guess that Seto Kaiba secretly finds his personal time with Yami in life or death ordeals as a somewhat of a strong bonding experience platonically that he wouldn't really be able to share that comradery with anyone else and seems to enjoy.
Again, this is not a shipping sort of post. I simply think that these examples signify toward those traits that would make sense to justify why he utilizes a FP (in this case Yami Yugi) in my hc of BPD along side the narcissistic traits he displays as well.
I think he a better example of someone how has these personality disorder(s) and how they gradually grew into a more mature person with it. I don't think there is as much healthy and respectful representations of cluster B personality disorders in media that immediately doesn't somewhat demonize and extend stigma to those who carry them, and I hope there continues to more examples of those have these mental disorder in years to come.
