Running away from a miracle.
He knew they couldn't keep running forever. Even if only one other participant remained, the grail would not be complete. And the Society had begun to take an alarming interest in his "Marble Phantasm".
Even if Shirou was an abject failure as a sorceror, his Servant wasn't. But they didn't dare use magic, and none of Shirou's experience and training as a high school student and semi-competent mage really prepared him for flight and concealment against powerful supernatural forces.
It was hard enough to hide themselves, and even the slightest hint of sorcery would betray them. Shirou thought sometimes that it had to be harder, way harder, for the woman walking beside him, who had lived in an era when magic was as natural as breathing. His fingers brushed the tips of her delicate ears, toyed with the strands of her fine, pale hair, stroking away the dust and ashes. She had made no complaint in their entire frantic flight across the countryside, even when they'd had to leave the roads and buses to camp out in the woods.
She had smiled at him, briskly brushing the dirt from her robes and folding their bedrolls with a practiced hand. Fleeing across hostile territory was hardly unfamiliar to her. "And at least this time I'm doing it of my own will," she had told him.
He hadn't had a good reply to that, even though he still cursed himself for not thinking ahead. When they'd first left Fuyuki, Shirou hadn't known where to go, because then from had been much more important than to. If he'd thought to find a car, maybe, or hijacked a small plane or something.
The last train they'd caught had taken them far enough, and with a few days of hiking they'd be in Osaka, where he might be able to steal a car, create a new identity among the millions of ordinary people. Maybe even forge passports for them to fly to some faraway country where they'd never heard of mages or grails.
They couldn't run forever, but maybe they could run for long enough. The knowledge that it was going to have to end sometime made him hang on to the present with tooth and claw. Her hand was warm in his, reassuringly solid and real. Beneath the starry sky they walked, uncertainties of past and future momentarily forgotten.