This was something Anno had done at the end of the previous Holy Grail War.
At the time, Anno's Spirit Origin had already been badly damaged. Even if he had remained there, there was very little he could still do.
The boy Emiya Kiritsugu had dug out from the ruins was on the brink of death, his life hanging by a thread. To save the child's life, and to save Emiya Kiritsugu one last time, Anno had given his Spirit Origin to that child—
Shirou Emiya.
This kind of Spirit Origin transfer was actually rather against the rules, but at the time, it seemed to be the only thing Anno could do.
So, in essence, Shirou Emiya had already become a Demi-Servant from that moment onward.
A Demi-Servant who had received Saber Anno's Spirit Origin—perhaps he could also be called Saber Shirou Emiya.
But perhaps because Anno's Spirit Origin had been too fragile at the time, or because Shirou had not yet been a mage, the power that had always lain hidden within Shirou Emiya's body had slept for a very long time.
Later, Shirou Emiya never encountered any real danger. Even after he began training as a mage, he was still excessively weak, so that dormant power continued to sleep.
Until—
Now.
"Shirou."
Anno looked at Shirou Emiya in astonishment, which soon turned into gratification.
The power he had left with this child back then had finally... been uncovered.
"—How is this possible!?"
The false Irisviel clutched the severed end of her arm, glaring furiously at Shirou Emiya, who was dressed like a knight.
Anno's iconic silver-white armor now covered Shirou Emiya's body. However, because the Spirit Origin had automatically adapted itself to the Demi-Servant, both its form and attire had changed somewhat, becoming better suited to Shirou Emiya's