It is all her fault. If she was there, none of this would have ever happened...
He knew that she was going to change his older brother from the day that he met her, no, from when his brother had first told him about her. He was young at the time, so the people around had attributed his uncertainty towards her to jealousy, and he supposed that he had believed them.
Then, she died.
He had felt nothing when she died; he had never actually gotten to know the woman. However, his brother was shattered by her death, and he did his best to be by his older sibling's side as often as he could.
But he failed. She had changed his brother, warped his mind. Now his brother, no matter what he did, pushed the world farther and farther away from himself, and spent days at a time in his house. He had begged his brother to stop, begged him to stop this blasphemy, but his brother wouldn't listen because he wanted to bring her back, even though they both knew well that Ishvala wouldn't do such a thing. The dead were meant to stay dead, and his brother soon learned that the hard way.
But his brother's mind was still warped, and he refused to give up on her. He abandoned God, and instead, began to worship the evil that is the Philosopher's Stone. Eventually, it was the evil that led to his brother's death, a moment he could never forget. One reason was because it was simply so horrible, seeing his brother in that horrible of a condition.
The other reason was the right arm of destruction that he now carried with him, the arm that reminded him of his mission from God, the mission that to this day, he still had.
Now, he was a wanted man, a criminal dubbed "Scar" by the military. He had killed ten State Alchemists, outrun the military at least twice, and had almost killed Edward Elric, the Fullmetal Alchemist.
But even so many years later, she could still ruin everything.
It was night, and he was in Central City's library, searching. He hoped that Fullmetal was there so he could kill the boy. Not only was he a State Alchemist, but he was researching the evil that was the Philosopher's Stone, and that could not be forgiven.
So, he was waiting. He knew he would have to wait for a while; Fullmetal wouldn't be here for at least another day, but he could probably use the time to find Marco's report.
Then, he saw her.
She looked slightly different now; she had lighter skin and wore makeup, but without a doubt, it was her. She had the same hair and the same face as before, and it was obviously her.
He had tried to destroy her, tried to put her back where she rightfully belonged, but her comrade-no, lackey got in the way, and he had discovered the hard way that they were immortal now, evil beyond all evil, Homonuculus.
Even after she had killed his brother and caused so much harm to him, she still lived. He couldn't understand it. Why would God allow such a heathen to live? Why did she continue to return to hurt him?
It's all her fault. And he hates her for it.
She will die. He promises, to nobody but himself, that she will die in the name of God.