one who represents the majesty of the gods
That's all I've got, really. Is there a kid more screwed up than Kamui? Well, I guess there's Subaru, and talk about a bad role model. And there's Fuuma. This series is full of unfortunate people.
Seishirou is actually the first to meet Kamui; I've never been clear on why exactly he attacked, but my best guess is that he was curious and simply wanted to test Kamui's powers. It seems the kind of thing he'd do. Aside from that, though, Seishirou mostly stays away from Kamui, and the one with a stronger relationship with him is Subaru.
Kamui latches onto Subaru immedately, and not surprisingly, either, given that Subaru is the one to pull Kamui out of his mind after Fuuma kills Kotori. The reason Subaru decides to help, in fact, is hearing just what Kamui's gone through, and remembering his own experiences with Hokuto; he clearly sees Kamui as a kindred spirit and decides to help him on account on that. So he goes within Kamui and helps him find his way out of his own mind.
Something I think is important to note here is that Subaru first meets Kamui as a child within his mind, and I do think Subaru always ends up seeing Kamui as a child — perhaps not as young, but definitely immature and inexperienced. He sees a reflection of his own 16-year-old self in Kamui and sees all the mistakes he made as a child. Subaru sees just how young and naïve he himself was.
Now, does Kamui develop feelings for Subaru? Possibly; this is a CLAMP manga, after all. Kamui is vulnerable, and Subaru offers him support when he needs it, and understands what he's been through. The opportunity is certainly there. That said, I don't think that Subaru returns those feelings, or is even capable of it. Kamui's age aside, Subaru is completely, obsessively focused on Seishirou.
Of course, then Subaru gets his eye poked out, and Kamui goes on a guilt trip the size of — well, Subaru's.
This parallel is brought to you by Tokyo Babylon.
En route to surgery, Subaru does manage to clutch Kamui and tell him that it's not his fault, because this is what he wished for. Obviously, he didn't want Kamui to feel as guilt as he did over Seishirou, and furthermore he knows that him losing his eye has nothing to do with Kamui. Of course, that doesn't stop Kamui from feeling guilty anyway.
Afterwards, Subaru manages to convince Sorata to take Kamui home and look after him. The real difference between Subaru and Kamui with regard to this incident and the incident in Tokyo Babylon, I think, is that Subaru only had Hokuto to look after him, and as much as she loved him, she could only do so much for him. Kamui has all of the other Dragons of Heaven, and they help him to heal from his incident. Kamui also has far more self-worth than Subaru; as you'll recall from the other sections on this site, the loss of Seishirou's eye causes Subaru to completely break down, while for Kamui it's yet another trauma to deal with on top of many more, and is thus easier to deal with.
By volume 14, I do think Kamui has started to accept that Subaru is fixated on Seishirou, and to more fully accept his own wish:
Kamui: I've caused you... to suffer such a serious injury... and I've gotten Saiki killed, but even so, I still can't give up on Fuuma...
Subaru: If that's your wish... my sister used to say that the happiest person was one whose wish was fulfilled. Happiness is different for each person. Even if... it seems tragic to other people.
Kamui: The only person that can make you happy... is the Sakurazukamori, right?
Of course, Subaru's wish is a death wish, and Subaru is trying to prepare Kamui for what he believes to be his impending death, so. There's that. He's also literally the worst person to give Kamui advice ever: "So you want to make a completely selfish wish that might make people hate you? Okay, I'll support you." But then again, that was the entire point of Tokyo Babylon and Subaru has clearly given up on doing anything that isn't making his wish come true; he doesn't care anymore.
Then volume 16 comes around, and, having fallen for evil!Hinoto's trap, Kamui is nowhere close when Subaru goes to face Seishirou. (Quick aside here: evil!Hinoto is by far my least favorite part of the series. Hinoto has a dark side, sure, I can buy that. But the plotline goes on forever and it gets dead boring at points. All of the dreamseers just end up repeating themselves over and over again after a while and all of the stuff with Hinoto gets very tiresome very quickly. She is a very frustrating character.)
Anyway, Kamui shows up in time to see Subaru with his arm through Seishirou's chest. Whoops. He pulls Subaru off the bridge before it can fall, and goes to him afterwards. Subaru isn't broken, but he does seem... well, empty. And he is, I think, without Seishirou. After all, his wish can no longer be fulfilled.
He does at least explain to Kamui why he wished to die — in the end, he just wanted to matter to Seishirou — and urges Kamui to make his own wish come true. Once again, Subaru is a terrible influence, but his words here are very important:
Subaru: Right now... you should be thinking about how to make your own wish come true.
Kamui: But what if... the thing I want the most will bring sorrow to someone else?
Subaru: There is no path you can take that will make everyone happy.
Now, this is obvious. This has been obvious from the beginning of the series. This is a manga about two opposite forces fighting for the end of the world. Of course there's no way to make everyone happy. But I think this ties very closely with Kamui's wish — the wish he holds at this point in the manga. Right here, his wish is to get Fuuma back, no matter what the cost. And, as we learn in the next few volumes, and through Fuuma's conversations with Subaru in particular, this is not Kamui's true wish.
So what is? Fuck if I know. I just want things to turn out better for Kamui than they did for Subaru, because otherwise, I'm not sure what the point was of all these parallels other than to show that life sucks.
In the last few chapters, Subaru shows up at Fuuma's side to urge Kamui to figure out what his wish is. Let's hope that if X ever continues, Kamui manages to figure out what it is.