The significance of masks and identities.
"I do not feel that circumstances---"
"Nah, it's okay. I promised." The assassin had given up his one chance of retrieving his name - at whatever the cost - to help Shirou save the last true "family" he had. Even by ordinary standards, he was owed something, though Shirou himself preferred not to think in such cold, practical terms.
Sitting gracefully upon the tatami mat, the Servant had removed his white skull-like mask. It was now lying on the table between them, a symbol of generations of fear and respect. Without the mask, the master of assassins looked less like a legend and more like a man, even if dark scar tissue clung to his face where his features should have been and his spidery limbs still moved as though their joints were unhinged.
And perhaps that was more accurate, that the Spirit called by the grail was more the mask - or what it represented - than the man who wore it.
He remembered the dreams, the memories of paradise that had perhaps never been quite real, that had sustained the assassin through the years. And then the initiation, where he learned the truth behind the Mountain, and returned to repeat the vicious cycle.
The part of Emiya Shirou that had its head buried in the concepts of "fair", "right", and "just" wouldn't let him ignore the implications of those dreams, nevermind that he hadn't exactly been in a position to do anything about them. Until now.
He held out his hand, hovering over the mask, and nodded to the Servant to begin. For a split second he had to resist the urge to recoil from the cold, claw-like hand that grasped his arm, but he managed, and few moments later felt a pulling sensation as though his skin was being scraped down his arm.
When he looked up at the man sitting across the table, his own face stared back, and he could feel the living pulse in the hand still clasping his arm.
"It's not much, but it's the only thing I've got from my old man." Shirou didn't expect the man to go with all the defender of justice business, but he still wanted to know that Kiritsugu's name would pass to one who would make him proud.
Shirou had always held on to the conviction that righteousness would win out, regardless of the situation. Now was about as good a time to test it as any.
The Old Man of the Mountain placed the skull mask across his features and silently slipped away. A moment later, Emiya Shirou emerged into light of day.