SPOILERS AHEAD
I have experienced abusive relationships and I'd hardly call Ryo and Hatsumi's relationship abusive. It was just another manga about growing up in love. I don't know why some people are taking Ryo's slave threats so seriously. Is it because he got so close, or because Hatsumi let him get so close? Or maybe, its because he wasn't the 4 year old making threats and a grown man? I see no difference, they were still young and inexperienced most importantly. The manga had people having physical relations left and right so I don't see why their close encounters were such a big deal. Ryo believed he could get whatever he wanted because of the way he was brought up. He didn't just sit there and wait to be fed though, he got whatever he wanted by any means necessary. I liked that about his character; he wasn't the stereotypical lazy rich guy. He put so much work into the relationship, some times I forgot he was rich and pampered. Many were turned off by his aggression, I found it hilarious that he had to try so hard to learn how to be gentle. He was also so calculative and plotting while Hatsumi was hardly thinking; the epitome of LOL's when a guy is trying so hard and the girl is not. Would you have read a book where a guy is sincerely trying to be gentle and kind? How many time has that been done? Wringing the dry cloth for more water = yawnfest.
If you think that Hatsumi was a pushover ready to submit, then you missed a vital trait. What Hatsumi needed was confidence. She received confidence when Ryoki chose her again and again, despite having more attractive and luxurious offers. Bigger boob size, more money, intelligence, mother's approval, you get the idea. Remember when she told off that girl? Yeah, Hatsumi had confidence in Ryoki loving her.
Hatsumi was jealous of her sister's good looks, and did not think much of herself. Then came Ryoki, a guy who wanted to possess her and have all of her attention to himself. He was quite in love with her, and I admired that. What he thought was love though and being in charge, he grew out of and learned how to better handle things. Eventually when he is fully sure of her loyalty (possibly after marriage) he will quit being paranoid and stop labeling. She did not realize how dedicated he was, until Ryoki chose a different more obvious approach. There was Ryoki's development - softening up a bit and learning how to love differently. Had Ryoki approached her like that in the beginning, the manga would have been boring and tiresome. Call it abuse, but I just think it was growth between two individuals.
Also for those who think that Hatsumi was still a pushover at the end of the series and that Ryo was still boss; you're wrong. You're not supposed to look at it that way. Ryoki learned exactly how to love her while still keeping his sassy attitude and natural leadership and Hatsumi gained the confidence she needed to be with RYOKI. She gained the confidence specifically to be with him, and nobody else. Hatsumi naturally fits the submissive type and that didn't change. Both personalities didn't change, but their approaches and views towards love and for Hatsumi themselves at the end of the manga did.
For those who think the author handled Shinogu roughly, I think your just bitter that the author chose to be very realistic at the end. I found it as incest, because she could never stop looking at him as a brother and could not find any chemistry between the two. I'd have rather seen Azusa and Hatsumi's relationship developed a bit more, though I liked that Azusa was the lone wolf at the end. Seemed to fit him. I think most here were turned off at Ryo's calculative way of learning how to love her, but lets not forget he also experienced an emotional roller coaster as well. Pissed then worried then jealous and even self reflecting at times.
Some might be mad that Hatsumi was so self sacrificing, and was willing to keel over to his demands and wouldn't stop him. Doesn't mean she has no backbone - it means she is a nice, self sacrificing person as displayed with how she handled her family relations. She may be on the dim side but she has a strong heart and is very humble. Sorry if the author didn't spell it out for you, or you cannot see yourself as being someone so self sacrificing. They're people like that in the world - I'd know.
To end, I thought this manga was done well and I would read it again in a few years.