He watches.
He watches as grey eyes turn to hate for the man that raised her after her father's death, mouth turning up into a sneer as she observes the king far off, burning another innocent. He knows she can see the king's death as surely as he can, though only she can see whose hand turns the blade. His or Hers.
He knows he should not think of the death of Uther, but he loves her. He even thinks she loves him too, but the hate blinds the love. Selfishly, he thinks that maybe if Uther was gone that maybe she would love him as she did before. Before they witnessed the constant burning of their kin, before the King decided that she should be married. Back when it was the two of them, lying in the forest, in the field he made just for her.
He is the light that contrasts her black. Though cut from the same tree, each turn to another path, sure from past experience that the other will lead to the doom of all Camelot.
He listens as she turns from the window, quietly sobbing, as she still refuses to let him see her shed tears. Still as she turns away, he grabs her chin and carefully wraps his arms around her as she sobs into his chest. He is not sure he can keep seeing her, as each visit makes him the Uther more. Idly, he wonders if in the future, they will stand apart, Camelot's people fearing her as they love him.
He doesn't know if he can handle it. Not without her. So he kisses her, hoping it will bring her to him, so he does not have to stand from her. But he feels, even now, that she is hardening her heart, preparing to leave him if he does not agree to go away with her.
He feels his resolve waver. He has been fighting her every step of the way, but now he knows. That no matter what he feels, he will follow her. He tells her this, and she smiles. The first real smile she has had since the burnings had began again. Maybe keeping that smile on her face is enough for me to betray the kingdom. No, not the kingdom. He betrays only Arthur. His brother.
"You know if we go through with this, we can never again set foot in Camelot. Arthur could never kill us, but he will never forgive us, either." Merlin said. "You'll never see him or Gwen ever again."
"It is for the best. If we do not kill him, Arthur will be the one to do it. He will marry Gwen, but be so angry that he will become the very thing he killed. By becoming Uther, he will drive Gwen to Lancelot. He will go on a rampage after that, killing all things he sees. He will have a final stand against Mordred, the boy-king, our son, and both shall die. Which we would not be able to stop, for the first he will kill is those closest to him. Us." She says, eyes flashing fire.
"If we succeed, Arthur will hate us but many will live. Arthur will find a journal telling him why his father burned, and he will put an end to all the killing. He will marry Gwen, but be happy, and the kingdom will be at peace. We will live and raise this baby," She gently lays Merlin's hand on her stomach. "Together."
He is convinced that what he does now is right, standing in front of Uther hands raised, eyes gold. Killing him is the only way for the world to live. For his child to live in a world where he will not have to fear for his life. So they say the words to end a life together. To make a better future.