Okay. I've seen people justify the relationship portrayed in this series by linking it to BDSM practices and dom/sub roleplay. Right off the bat, I'm going to say I know very little about BDSM. But, as I understand it, it has very clear rules and sets firm boundaries in order to guarantee that both parties involved feel in control of their body and their autonomy. It uses safe words, and always respects consent.
This was not present in this series. There was no consent. Segasaki was grabbing Yoh and throwing him on the bed whenever he felt like it, without asking him if he even wanted to do that at that moment. He even ties Yoh up at one point, without consulting it first.
I'm confused about how they wanted me to feel about this couple. Should I ship them (I don't)? Should I be concerned for Yoh's safety (I was)? Should I find Segasaki's attitude attractive (I don't)?
Honestly, this was just incredibly hard to watch.
Yoh had no development at all. He's a very meek character, very soft-spoken, lets others walk all over him, and is easily influenced (or rather manipulated). He doesn't question Segasaki's possessiveness of him. He doesn't fight back when he's forbidden from seeing any other person that isn't Segasaki, be it a man or a woman, a friend or an acquaintance. He cooks for Segasaki (whatever food the latter asks for), and sleeps with him when the other feels like it. He doesn't even KNOW Segasaki likes him until the last episode or so - when Segasaki tells him directly (and Yoh thinks 'I thought I was worthless'). I'm just- this is so bad? Someone please save this man??
Yoh also never emotes. He has no emotions other than surprise, submission and slight joy (let's mention that the happiest I've seen him was when he was hanging out with his friend's husband). There's nothing else.
Segasaki is just despicable. Maybe it was intended, maybe it wasn't, but I just can't stand him. I've already said that, but he's so possessive and controlling and kind of uses Yoh like he's his personal toy. He's all over him when he's jealous of the 'editor' (which doesn't even exist), then ditches him and ignores him after a misunderstanding (and doesn't let Yoh explain anything). He tells Yoh his life is 'his', warns him not to 'run away' while on top of him and tying him up, and ends up blaming the misunderstandings they've had on Yoh (apparently he does things on purpose to confuse Segasaki and make him jealous. ...Okay).

So. I guess I didn't like this series. I actually kind of hated it. If its intention was to portray a toxic relationship, I don't think it was made clear enough. And if it was meant to represent BDSM, I think (again, not an expert) it was done poorly.