Funny how opinions on yaoi can differ so much. I just read three manga in a row, which this one being the third, and didn't think much of the other two - cute, but ultimately boring. This one, however, I loved. Then I went to read the reviews and they all contradicted my opinions, which the other two having 9s and 10s, and this one being dragged. Well...if you like fluff, of course this isn't for you. For me, however, it's exactly the type of thing I look for in manga.
The thing with Tsume to Toge is that you have to understand the fine line between hate and love, and how an obsession could make someone fall in love without realizing what they are actually feeling. That's may be a difficult concept, so it's not a light read. I also feel like previous reviewers didn't understand some of the story.
I'll break it down: Kazuoki gets pushed down the stairs by Shuuji. Kazuoki thought it was intentional, but Shuuji didn't actually mean to do it. Kazuoki spends the following 10 years obsessing over Shuuji and how he was going to get his revenge. He ultimately comes up with a plan that's beneficial to him, which is to take a compromising picture of Shuuji that he can then use to blackmail him and his family. Shuuji, on the other hand, has never forgotten the accident with Kazuoki, which led him to feel so guilty that he started blaming his father for having a lover and leading him to be out of control and causing that fall down the stairs, so he is basically estranged from his family when they meet.
As Kazuoki is acting out his plan, he starts sleeping with Shuuji and spending more time with him, so not only does he get to know him better, but his real, caring self also comes out at times. He doesn't understand his own feelings. He's been obsessing with Shuuji for ten years...looking at him from afar, admiring him and hating him for things he wish he had. He hasn't thought of anything else all that time. Naturally, he was in love, he just hadn't realized it. If you can't stop thinking about someone for 10 years, it's normal that it'll turn to love.
Shuuji falls in love too. Yes, there is dub-con, though I wouldn't say rape. That's also a very fine line in yaoi. Kazuoki does jerk him off against his will, but everything else since was consensual. He hides it under the blackmail excuse, but he actually lets Kazuoki into his life because of his guilt that he wants to atone for. Slowly and also because of his previous feelings, he starts noticing the little things Kazuoki does for him, his presence and absence... and starts falling in love to.
My favorite part is the realization of their feelings, because it's sooo angsty, and that's exactly what I search for (and rarely find, especially well done) in yaoi. In fact, I'd say the opposite of everyone's comments here: this was very skillfully done and I haven't read anything that good in a long time. The way Kazuoki's obsession with Shuuji slowly turns from hate to love is very subtle, yet detailed.
Shuuji is alright, not my favorite type of uke, but not the worst, either. Just normal. But Kazuoki is definitely my type of seme. Angry, pushy, frustrated, bad at expressing and understanding himself. Just perfect!
The art is also lovely, the sexy scenes are great. I would actually highly recommend this. The only reason I won't give it a 10 is because there could've been an extra chapter. I would love to have seen Kazuoki saying "I love you too" to Shuuji.
And as for Kazuoki being Shuuji's actual half-brother,
at the end, when he's on the phone, he says he will pay back all the university fees, which implies the results of the DNA test were negative and, therefore, he is not part of the family, so he owes that money back to Shuuji's father. I agree that should've been made clearer by the mangaka.