Souma Kanzaki

It's not easy to recognize it if you're not looking for it, but Souma really is a bpd mf and I'm here to tell you why.
Souma in meteor impact is actually one example I believe to be of him splitting even if there are other factors for his behaviour. Especially when he went off on Kuro and Keito about them being sloppy and unfocused; he was brutal, and still acknowledged that he was attached to them. It read like a typical devaluing moment to me. What also stood out to me in this scene is once Keito complimented him a bit, he eagerly rejoined Akatsuki and it seemed like his episode was over, like the anger just dissipated because he no longer felt like he was being abandoned.

On the topic of devaluing, Souma has a strong distaste for Kaoru which is obvious. Despite the fact that he can acknowledge he has good traits (see: Aquarium), he is unable to see him as anything but negatively, thus meaning the bad overtakes the way in his thinking as opposed to having him see Kaoru as a grey area. He is often hostile and violent with him, which is an example of him not being able to control himself with those categorized negatively. However, he does have moments in which he refers to him with -dono, so he’s capable of being civil with him when necessary.

Now, Souma is able to be apart from Keito and he is able to acknowledge that he’s busy and doesn’t always have time for him, though he states in the story School Trip that being apart upsets him to the extreme and makes him cry, he just tries not to think about it most of the time or internalizes it. Souma is jealous (though not maliciously) when Keito gives affection to others. He strives for his attention and approval. In addition to this he declares him as his lord, and vows loyalty to him, showing heavy attachment. He also worries heavily about what Keito would think of his actions quite a few times in stories such as Billiards, and fears upsetting him.

From what I’ve seen so far Souma hardly sees Keito in a negative light, and avoids being critical of him especially after Meteor Impact (which also holds the only exception I’ve seen, where I believe he splits). He clearly sees him in an idealized light throughout almost every story. However, this is not to say he is incapable of following/feeling what he personally believes to be right or wrong. In addition, Souma easily deems people threats to the student council, and by extension, Keito. He is not hesitant to explicitly say so either. He shows violent tendencies to the people he deems a threat, and has even admitted at one point that he "wanted to try cutting up an actual person with a Japanese sword".

Trigger Warning for seppuku/hara-kiri and s/lf h/rm discussion below
To me, the fact that when he has upset someone he offers to commit seppuku, seems very much like a black and white thinking situation. He either is forgiven, or he should die, which is extreme. (Seppuku is a samurai ritual, though the situations and ways he goes about it are not the same as the actual tradition.)

In addition, to me it does count as at least akin to a self harming behaviour because he is willing to hurt himself, especially when it comes to upsetting Keito, Souma offers to commit seppuku for him more than anyone else.

This (and the aforementioned School Trip story) leads me to believe he would self harm “off screen” over upsetting Keito and possibly thinking he's going to hate him and pmight leave him, but that is entirely my own speculation so take it with a grain of salt.

To end off, here's the holy trinity of Souma bpd quotes:
"Indeed! I shall be good! Therefore, I ask you not to abandon me, Hasumi-dono! I still wish to participate in Akatsuki together with you, Hasumi-dono, I shall even deal away this Japanese sword for a brief period, so…!”

“Fushimi-dono is in pain due to his lord, correct? I myself understand that feeling all too well. Once I am separated from my lord, it is then that I lose my feeling of being alive. In fact, I am brought to tears. Uwaa~n!!”

“Hasumi-dono, I am most deeply sorry for my lack of resolve! Now that I have fallen so low, I will perform hara-kiri to demonstrate my most sincere apologies!”

==== If you'd like to check out my powerpoint (which is less eloquent but has screenshot proofs) feel free! ====