Shiro didn't need to be close to Rin to know how much this hurt him to say. However, being so close to him broke down every wall Shiro ever built. He didn't want to see Rin cry, and knowing he was the cause of it was like a dagger right to his heart.
He hated how real it all sounded. How to the T the attempted plan had been. Everything from contacting Mephisto, getting him out of there, all of it with the sole goal of protecting Rin. God it was so real. It was his plan, the one he'd come up with for the worst possible scenario and it happened. Shiro's hands rested on his knees. It took everything in him not to bawl them up into fists. He never wanted any of this for either of his sons, yet here they were.
Shiro kept Rin's gaze, even as the speckles of flames ignited and grew along the teen's body. Slowly Shiro reached out and plopped a hand firm on Rin's head. He pulled him into a tight hug, "It's ok. None of that matters now, I'm here." He wasn't sure exactly what to say. It was a feeling he got almost everyday, trying to guide these boys, but this time it felt like the first time. The same it had 15 years ago after she'd died and he was left sitting all alone in the snow, with the two of them in his arms. Lost.