This is what stood out to me on first watch:

Skin is almost aggressively trans-coded through its body horror motif, and

Stylistically, it's an artistic tribute to DPR Ian

So much has already been written about body horror and the trans experience by people better versed in both writing and queer studies than me, so I’m not going to attempt any kind of scholarly essay here on why it’s so important as a trope to so many trans people, myself included. It also isn’t something that all trans people identify with and intersects with so many painful things - dysphoria, internal and external transphobia, medical intervention, etc.

What I will say is that this is how I found out I was trans:

When I was very, very young, I realized that something was different about me, and that it was something so deeply wrong (I thought) that no one, absolutely no one, could ever find out because they would see me for what I actually was: a monster. The way I felt (Not a Girl) and the things I wanted (Not to Be a Girl) were so grotesque that it was a requirement, literally an imperative, that I bury them as deeply as I possibly could and, god willing, never let them see the light of day.

Unfortunately, as I discovered in my early 30s, dysphoria is a living thing that, for me, refused to stay buried. My coping methods for dealing with it began to fail, one after another, and eventually I was having dysphoria-related panic attacks so frequently and severely that my survival depended on addressing the root of the problem. And in order to do that, I had take apart my identity piece by piece, try to understand it, and reassemble it into something I could live with. It took months. It took reading so many books. It took therapy. And eventually, it took transition.

How does this relate to body horror and Skin?

Well, one of the things I was drawn to from a frighteningly young age were stories where things happened to peoples’ bodies that changed them, usually against their will and usually painfully. As a theme, it’s dark, it’s messy, it’s often violent, and if you’re living with a level of fear and internalized transphobia so intense that it feels like its own form of violence, it can be cathartic. And for me, the terror of being trans came from two directions: internally, from a puberty that had already changed me in ways beyond my control, and externally, from what felt like a foreign, threatening force that wanted to change me yet again when I did not want to be changed.

Or rather, I did not want to want to be changed. 

Only by doing the actual work of deconstructing my transphobia (still in progress, possibly work that will continue for the rest of my life) did I understand that that outside force was in fact not outside at all, nor was it foreign. It had come from me and was a part of me that couldn't be excised, mentally or physically, and I had the privilege and somewhat limited power, given certain societal, medical, and financial constraints, to address it as I saw fit.

(As an aside, this is also why conversion therapy does not work and will never work and is actual violence. Protect trans kids.)

So the way body horror relates to transness can, for me, be summed up by one question:

What is more monstrous: your current form, or what you fear may be your true form?

And what am I seeing in the music video? Seonghwa in dialogue with two things: the monstrous, and the feminine. To be clear, these are not equivalent. The feminine can be monstrous and there can be great power in that, but I don’t think that’s the reading here. The monstrous thing is the question. It is the uncertainty. It is acceptance and undertaking the change. (I think there’s also more to be said about how we define what is monstrous, because that’s also important, but that’s a subject for another day.)

Skin starts with something literally spreading under Seonghwa’s skin, dark veins snaking out like he’s been infected. Has he been invaded by something foreign, or is something manifesting that’s intrinsic to him? Then he rips something off his back, and later we see him and several women with scalpels literally studying this thing in a laboratory. What are they looking for? What is he trying to understand? Textually, he’s examining his own flesh. Symbolically, he's taken what appears to be that monstrous, incongruous piece of himself and is dissecting it through the expression of his art, which is his primary outlet.

Who else in Seonghwa’s sphere is known for explicitly doing this? DPR Ian, who uses his music and maximalist music videos to visualize his struggles with his mental health. Seonghwa’s outfit at the end is a DIRECT tribute to those videos, which feature DPR Ian in the guises of different aspects of his own personalities. I’m serious, go watch Don’t Go Insane if you haven’t already seen it, it’s great. I think it’s possible that this is his way of thanking DPR Ian for inspiring him to be brave enough to make this kind of art.