What was Saber King Arthur's strongest Noble Phantasm?
Faced with that question, many people's first reaction would be Excalibur. However, with just a little deeper thought, that "strongest" would be replaced by another Noble Phantasm—the scabbard!
The scabbard was Arthur's true strongest Noble Phantasm. Its transcendent defense could isolate even the Five Magics, naturally placing its holder in an undefeated position.
This was also reflected in Type-Moon's story of King Arthur. After King Arthur pulled out the Sword in the Stone, he/she was almost invincible in battle. Under his/her leadership, Britain moved toward upheaval. Yet, by sheer coincidence, after Arthur's scabbard was lost, he/she suffered an unprecedented defeat—and at that time, the Sword in the Stone that symbolized the throne was still in his/her hand.
So the moment Shiro saw Arthur, an idea formed in his mind. He had no intention of touching the Sword of Promised Victory in Arthur's hand, nor did he have the ability to. Of course, he also did not have the ability to analyze the scabbard. Shiro merely wanted to gain a rough understanding of how the scabbard defended. Judging from the description of the scabbard, when it unfolded, its holder stood within Avalon, that special small world.
Because for Shiro, who was currently analyzing the world, this was an extremely perfect material: something above the present world, yet far smaller than the present world.
So at that moment, Shiro suddenly discovered that Youye's aura was extremely similar to the scabbard's.
Combined with Arthur's attitude and Youye's own special nature, how could Shiro still not understand?
Youye was the scabbard!
And it was not like Shirou's situation, where the scabbard had been buried inside his body. Youye herself was the scabbard!
This was somewhat unbelievable, but it was not impossible. If Youye was the scabbard,