It would be categorized as rape. Yoru was sold into slavery and then forced into prostitution. Amran paid for sex with Yoru and then purchased him for permanent use. He did not buy Yoru to free him but to possess him. He puts a new pair of shackles around his ankles. Does not offer Yoru the possibility of freedom. He even ties Yoru up and assaults him just to get him to speak to him again. Honestly, there could have been a redemption ark I guess. But this was poorly executed. Just seems like Yoru has stalkholm syndrome. Anyways, they're not in an equal power relationship. Yoru is still a slave while Amran is his master. Just bc he says he's been in love with Yoru since forever ago, does not excuse his actions.
(Not arguing with you. Just posting what I got from the story.)
The art is so incredibly beautiful I was just put off by the way they “fell in love”. Idk I think it’s just a weird premise to have the ml to pay to have sex with him, then buy him and essentially force sex on him, (not explicitly rape but dubcon if I had to categorize), all the time and then the mc realizes he has feelings for the ml. It was still a good read and I would say it’s definitely worth checking out, just thought I’d share my two cents.