why all the hate towards the older brother?!

I don't think that the motoharu is calculating and manipulative from the get go. He especially didn't plan out the events to occur the way it did. Similar to what otlcryman posted, I think what the last conversation about being a good older brother is meant to show that he wasn't as ignorant, hopeless, or innocent as the readers might have assumed him to be. He was aware of akio's feelings and actions but in no way tried to influence him towards one way or the other. In fact, you saw how encouraging he was towards the "girlfriend." I think one reason why he chose to keep all of this hidden is because he blames himself and feels ashamed for making his brother, who he is so proud of, this way. Thus, when he was raped by the akio, it came as no surprise to him no matter how much he tried to stop it. I mean, he probably was slightly prepared for the day akio will attack him while desperately hoping that that day will never come. He stopped bringing guys to their place, then stopped selling his body altogether, and finally managed to get a job and stuck with it. Perhaps the fact that he brings up masturbating to the rape is his attempt to destroy this image of him as a helpless victim and akio as a wild, crazy rapist. After seeing akio again so many years later, I think he realized that his act of running away did more harm than good to akio. He also probably still feels very guilty for how much he ruined his brother's life, and so, you see him accepting akio's feelings. Now that he has fully embraced his situation, the readers get a glimpse at how similar and twisted the brothers are (it wasn't only the younger brother who had such twisted thoughts). He wants to play the role of a good older brother in order to secure his position alongside the younger brother. He also probably doesn't want to be abandoned now that he has returned to a world where it's just him and akio again. Plus, the ending did not feel like motoharu was saying "mission accomplished"