Atsumu was forced to penetrate Azusa.

Tatsumi's lover (Tatsumi is Karino's step-brother) suddenly picked a fight with Karino, ready to kill him because Tatsumi said he wished the pressure in his life would disappear, it was awesome. Karino is an ass, so that served as nearly instant gratification for me as I was reading. Thanks for that one Ogawa-sensei. ^__^v

It's obvious by chapter 4 Karino's the main love interest. But I kind of feel like Kuse and Kusakabe have been tossed by the wayside a little as characters. It's like the mangaka was developing them and then part way through the first chapter figured out who was going to turn on Azusa and then pushed them into the background.

As for the ending of the first chapter, it really impacted me. I have read a lot of manga that have had rape themes in them, but this one stood out to me, a LOT. I felt thoroughly empathetic with the main character and fully understood his shame and anger. But then the story started to go towards him having feelings for his rapist and honestly I'm incredibly disappointed. I am never the first to complain about rape=love in a BL, but here, I can't help but feel let down.

Karino

I'd say I'd still like to see Azusa not get with Karino, but I feel like his character's changed too much in the wrong direction to recapture the feelings I had in the first chapter.

I would just like to add a bit to my earlier comments. I think the reason I’m so perturbed by the rape=love theme here is because the mangaka does such an amazing job of characterization that it feels too realistic to work with these characters. Azusa was pushed down the stairs, bound, blindfolded, gagged, raped and his reaction upon finding out it was Karino was to repeat that he’ll kill him over and over. That works perfectly for his ego and stubbornness.
Even afterwards when the mangaka reveals he felt pleasure when he was originally raped works. Just because someone feels pleasure doesn’t mean they weren’t raped. Rape is violence, dominance and a pure power play. And that’s exactly how it comes across in this story in the beginning. Not love, but violence. Karino wanted to dominate Azusa and that's what he did - taking what he wanted and using violence to shove Azusa off his high horse and into the mud at his feet.
Karino might be obsessive over Azusa, but he doesn’t love him. He treats him like a toy and he’s still too immature and self-centred to even care about Azusa. He seeks fulfillment for himself (and that includes moments where he has seemingly been kind to Azusa – don’t forget he’s still holding all the cards and doesn’t actually care about Azusa as a person but more as a plaything to enhance his own personal life. Yeah, he’s kind to Azusa when he’s feeling down after getting punched, but Karino doesn’t want Azusa to be completely broken. He won’t be any fun that way).
Another reason I’m not fond of Karino as the main love interest is because I feel there’s a bit too much of a discrepancy in his character from the beginning of the first chapter to what we later on learn is his true character. Seriously, he’s the one who should get the Oscar for acting! The way he blushed ‘like a virgin’ in the beginning and some of his facial expressions don’t match at all to the point that when I reread the first chapter, it didn’t feel like the same character at all. If Karino had turned out to be obsessively crazy in the sense that he wouldn’t let anyone but himself have Azusa, I could believe the two sides to his personality. But that’s not his true character at all.
Karino is calculating and bored with his life (actually, he has a lot in common with Yagami Light from Death Note). He finds relief and entertainment in Azusa, not an obsessive love that puts Azusa at the centre of his life (he's the only one at the centre of his own life). If Azusa really did become like how he acted in the fourth chapter – all obedient and pitiful, Karino would lose interest. Because Karino wants to play with someone who acts prideful and domineering the way Azusa has – it doesn’t necessarily have to be Azusa. And that’s only at school. He doesn’t want Azusa in his life. What Azusa thought – about Karino wanting to eventually leave this behind at school when he steps out into society – is completely true (to this point in the story anyways). Karino isn’t expecting some kind of relationship with Azusa. He is just trying to get more excitement out of life for his own sake.
So, I’ll reiterate again and again, even if in the future the characters change, right now Azusa has been falling in love with his rapist for no real reason but plot development (at the expense of the great characterization that the mangaka did on his particular character) and Karino does not love Azusa but obsesses over him as a favourite toy. And rape=love here bothers me so much only because the story started out so well that I am holding it to a higher standard than most other BL. The mangaka did a great job and in turn, because she did a great job, I’m disappointed. It’s perplexing.

I totally call that Kuze killed the bunny himself. That lovable sadist. The best of all though is that Atsumu is proving himself to be more than a wimpy character. I can’t wait to see what will unfold in the near future for them. Atsumu is going to be a great character, I can so feel it.