I truly felt bad for the seme

Reading the prequel helped. His parents never gave a shit about him or his adopted brother. They were "decorations" for a "perfect politician's family" and nothing more. He could have had sex with his adopted brother, no blood relation and all, but he was too self-absorbed in his own isolation and neglect from his parents when those desires developed. He was the perfect everything, student, child, businessman, all to gain attention from his parents, but they denied him even that reward for his work. If he brought a scandal like sleeping with his brother, all his work would be for naught. He blamed his brother for awakening those feelings on him. Therefore, he chose to vent his frustration on his brother with emotional and mental abuse. He then graduated from emotional abuse to physical abuse when he moved from home and could pick up strangers. Nothing excuses his violence, but a past like his can explain it. He wanted to be loved so desperately by someone, anyone, his parents, his brother. Then the uke came along and patiently loved him, regardless of his terrible and violent personality. Something no one had ever done before. Everyone else had set conditions on their love and when he failed to meet those conditions, or even when he succeeded, they withdrew it. The uke didn't. It saved the seme.