Aziraphale watched Castiel become more and more agitated, finally taking hold of the other angel's hands so that he couldn't harm himself. He pulled Castiel to him and wrapped his arms around him, just holding him and doing his best to comfort him. "Anna is safe," he promised, "and she will remain so. I would never allow her to come to hard, brother. Never."
"You need to calm down and focus, Castiel," he said softly. "You are safe and no one will harm you. I would not lie to you...you know this." One hand smoothed Castiel's hair gently, while the other remained wrapped low around his back. His hand moved up to run along one of his brother's wings, stroking it softly as he whispered comforting words, promises of safety and reminders of how Castiel was loved and not alone.
"I'm not leaving you, my dear," he whispered. "I'll never leave you." He would stay even if Archangels really were coming. He'd be no match for them like this, but he would stay for Castiel's sake. "Just calm down and focus." He needed Castiel to realise that all of this was in his head, but he didn't know how to make him believe it. He just continued holding him, resting his forehead against Castiel's as he spoke quietly.