I personally wanted the black haired seme to gain the love of the MC because the concept of siblings having a relationship really concerned me. I know the black haired seme was blackmailing the MC and was abusive but to be honest that's the plot of like 70% of all shounen ai, is it not? The story went in every direction and it was kinda weird. It couldn't really stick to a specific type of story.
That was the fastest plot development I've ever seen. So anticlimactic.