Shiro slipped into the Gehenna gate almost gracefully, his fall one moment that stretched itself into an eternity as it etched itself in Rin's memory. He stared, unblinking, at the body that floated in the gate for a moment before a small scream escaped his lips and Rin pulled himself closer.
Searching his face for and sign of life, and listening to his heart for a beat yielded no results. Rin was forced in that moment to confront a truth that shattered his fairytale life, one where demons existed only in fiction and the bible, one where his inability to hold down a job was his greatest concern, one where he himself was a human, you see, now his father was dead. It was all real now.
"No..." Rin whimpered, shaking his head. He didn't want it to end like this, Shiro had died trying to protect him, and there was nobody left to save him. There was nobody left to look up to. The only thing Rin saw when he did look up, searching for any other way to escape, was Kurikara.
Resolve pushing away that helplessness, Rin gripped the handle and pulled himself up. "Hang in there," he told Shiro, believing that maybe a doctor could fix him, that if he could get himself out of this then anything would be possible.
The blade slid out easily enough, and Rin lifted it above his head, frowning but still feeling sweet freedom just around the corner. Then a wave of exhaustion hit him, being dragged down again from that high.
He swung the blade down at the gate, but there was no force behind it. He hadn't even noticed that he was down to his waist. Rin tried to destroy the thing again but he could barely keep his eyes open. He shoulda just thrown the sword as far away as possible... Then, he passed out.
It takes a lot of energy to transform into a demon the first time.