This story and the comments about it caused me to come to an epiphany of sorts in regards to sadomasochism, more specifically, I think I already knew this on some level but this story caused me to actually think about it and put it into words. So, I came to the conclusion that there are three broad types of sadomasochism: physical, pride, and emotional is what I have dubbed them for now. These can exist independently but are by no means exclusive of any of the others. Some others in this thread seem to have come to similar conclusions but none really went in depth which is why I will since I feel this very much helps in understanding this story.
The first one, physical S&M, is probably the most iconic, the one most people think of when they hear sadomasochism. This is the enjoyment of giving and/or receiving physical pain. I don't think this one needs much more explanation, I think most people already understand this one well enough. Iori seems to be a physical masochist and Kanan is very clearly not a physical sadist.
The second, pride S&M (I don't particularly like the sound of this one, so I am open to ideas for alternative names), is probably the second most well-known type though seems to be, in my (admittedly quite limited) experience, the most common form. This one is about humiliation, being demeaned and degraded. This one is also fairly straight forward and isn't relevant to this manga so I won't go into further detail on it.
The third and most important type here is emotional S&M. This is the one that seems to be the least common, or at least the least acknowledged, type and is about emotional anguish. This is the one that I would like to be able to explain more thoroughly since I feel many people don't seem to understand it, or the masochism side of it anyway, but I can't because this is the only one that I can't really seem to understand myself. I am somewhat of a physical and pride masochist myself and I can sort of understand all three forms of sadism, but I can't get my head around how someone derives enjoyment out of their own emotional suffering. I am genuinely curious if anyone has any ideas on this.
Even though I don't really have a good explanation of emotional S&M it is the one that I feel is most important to this story as both of the girls seem to fit in here, Iori seems to be an emotional sadist while Kanan is an emotional masochist. This is important because it is what separates their relationship from outright abuse. If Kanan weren't an emotional masochist, if she didn't get enjoyment or fulfilment out of the anguish she feels when made to hurt Iori than this would just be outright emotional abuse. It is also part of why I don't believe, as one person suggested earlier, that Kanan is actually a physical sadist and just hasn't come to terms with it yet. Furthermore, I feel that Kanan actually being a sadist would make this a much more tragic story because what that person failed to acknowledge, is that Iori outright states that she does not want her partner to enjoy hurting her, in fact, she seems to want a partner who actively dislikes doing so (which to me potentially indicates emotional sadism). Thus if Kanan did come to enjoy causing Iori pain, they would likely break up leaving them both unfulfilled.
Another thing that fully clicked thanks to reading this is just how much S&M is conflated with dominance and submission. I noticed several people in this thread seemed to be unsure who was the dom and who was the sub. While I think many people have come to realize that being a dom does not mean being a sadist and that being a sub isn't the same as being a masochist, it seems that some haven't fully realized that the reverse is also true, excepting cases where someone is a switch or a sadomasochist (both sadist and masochist). I found it quite clear that Iori was the dom and Kanan the sub, all of the sexual/sadomasochistic interactions between the two were both initiated and directed by Iori with Kanan just doing what she was told, Kanan even thinks at one point that she can't resist Iori's commands.
p.s. Sorry for the wall of text.
