As a willpower, Alaya rarely acted personally. It usually had Guardians work for it and correct history, but that did not mean Alaya was incapable of intervening.
For example, the reason Heroic Spirit EMIYA, Red A, came to exist was because years later, Shirou Emiya faced a nuclear power plant leak. To save over five hundred people at the plant, he made a contract with Alaya and became a Guardian.
Thanks to that, those five hundred people were saved. However, although he had made the contract, Shirou Emiya was already near death when he approached the reactor core that was about to collapse. So even after making the contract, Shirou Emiya only had two years left to live.
Although Alaya usually got something for nothing, sometimes it did pay up.
Although Alaya had not personally saved all five hundred people at the time, afterward, Shirou Emiya changed as though possessed and saved people who should have been beyond saving.
There was no way that had been accomplished through Shirou Emiya's efforts alone, right?
It was impossible for Alaya not to have intervened.
"This contains all of Justicia's remaining consciousness. Justicia truly possessed the Third Magic, so this does count as giving you the Third Magic. And I told you beforehand that it was a reduced version of the Third Magic," Alaya emphasized.
Justicia was indeed a holder of the Third Magic, but she was not quite the same as the complete Third Magic.
She was a homunculus created by the disciples of the Third Magician, and also a homunculus that had genuinely recreated an individual possessing the Third Magic.
It was merely that she had appeared by coincidence.
Justicia was equivalent to the Third Magic, and Justicia's remaining consciousness was equivalent to a reduced version of the Third Magic...
Theoretically