Assassin of Red's Fortress Noble Phantasm, Hanging Gardens of Babylon. Though on the battlefield, this fortress was the only place ruled by silence and calm.
"—Now then, Master. Was that part of your calculations?"
She smiled nastily. Shirou Kotomine gazed down at the phenomenon that had just occurred with an unusually grim expression.
"Unbelievable! Saber of Black has revived! Goodness gracious, it's a great miracle worthy of a saint! Truly, [Hang up Magic]!"
In response to Caster of Red's mutterings, Shirou shook his head silently.
"No, it isn't a revival... If I had to describe it, that is closer to a possession."
"A possession?"
"...Among Servants, there are also those who can cause strong effects on the bodies of their Master. Normally, the relationship between Master and Servant is the same as between owner and familiar, but there are those who possess skills that make it possible to share bodies. In those cases, the Master becomes an existence close to immortal. Of course, only for the duration of the Holy Grail War... And most importantly, it doesn't mean that their battle power increases, so the only Servant they'd be able to fight is Assassin."
"Wait. No matter how I look at it, that there is different. He isn't a Master, and he definitely isn't a Servant."
"Yes. That's why it's a possession. Most likely, he's summoning Saber of Black with the abundant prana of a Command Spell. Of course, normally it would be impossible even with a Command Spell, but—"
Saber of Black and Saber of Red were fiercely clashing against each other. It was an impossible battle even in myth between the 'Dragon-Slayer Siegfried' and Saber of Red.
"That homunculus alone is an exception. He has something connected to Saber of Black within his body. I don't know if it's a part of Saber's body or a holy relic of his. In any case, by using that as an intermediary, he's making Saber descend from the Throne into his own flesh."
"Impossible... We're not such low-class evil spirits. We're Heroic Spirits, you know? The purity, density, strength, solidity and every other aspect of our souls are completely different. Something like possessing someone's physical body and giving them a Heroic Spirit's abilities is impossible."
Assassin of Red was correct. If Shirou's words were right, then that was a 'shell', a being who wore the body of Saber of Black. But that was impossible. The physical abilities, magical abilities and, of course, the soul of Saber of Black—no, of any being that was called a Heroic Spirit was incomparable to that of a human's.
"If a body is possessed by a Heroic Spirit, a human's soul wouldn't be able to endure it. To say nothing of the soul of a homunculus like him."
"It's precisely because he is a homunculus. Their souls are very young and therefore pure, as such they won't be dyed by anything, and their bodies can endure any kind of transformation as well."
In the first place, a homunculus was a 'molded' entity using Magic Circuits as the foundation. Since they had no accumulated experience like humans did, their souls were pure and sturdy like an infant's. A human who had lived twenty years would have twenty years' worth of accumulated experience, and that experience would sometimes produce magnificent strength under critical duress.
But, when you possessed another person's body, that accumulated experience became jammed and obstructed as if by white blood cells. That other person's accumulated years of experience and your own accumulated years of experience would clash due to lack of compatibility.
