I get it.

I understand a lot of people like this manga but also please consider this. This boy was minding his own damn business and gets dragged into this so called 'slave play'. He is not only mentally abused as well as physically. This boy might have serious trauma. The seme is an asshole who has not only taken his right to his body but also passes him onto people. he is called a sex toy. as human beings we need to understand that when someone goes through pain we must not find pleasure in it. What i'm trying to say is there's something known as 'rape play'. but the difference is they both consent to it. They don't actually force it.
He is forced.
And what suddenly the uke gets a little proactive and the seme's heart goes 'badump'? He made him go through so much and badump?

I cannot empathize with the people who like this manga. You ask why we read it till the end? We want to know if there will ever be a redemption. We want to know if karma will get back at him. but subconsciously we know that the uke is just gonna shower him with unconditional love and forgiveness and that the seme will never realise his mistake. What train him? He is just purely an asshole who deserves to get beaten up, not only him but everyone else too.