Brynhildr's Noble Phantasm failing to kill Sigurd was the most irrefutable proof that he was not Sigurd. Holmes then proved from several angles—the enormous sun-like presence in the sky and the mountain of fire in the north of the Lostbelt—that the enemy was Surtur, King of the Fire Giants.
"The ruler of this Lostbelt is Queen Scathach-Skadi. Yet with her here, a volcano appeared. That is extremely strange. The only possibility is that even Her Majesty has no way to deal with those flames."
"So that's how it is. Is this how a detective thinks? I wonder how Lord El-Melloi II and Holmes would react if they met."
After hearing Holmes's explanation, Shen Fei finally understood some things. While he had been marveling at the Lostbelt's spectacle of ice and fire, Holmes had already seen the truth hidden beneath it.
Unlike the original situation, where Holmes had his arm severed by Sigurd and was afflicted by the Rune of Death, leaving him unable to think clearly, Holmes was uninjured now and naturally had more time to investigate.
Shen Fei had crammed some knowledge of Norse mythology, but it was only knowledge. Naturally, he did not understand it as well as Holmes and the others.
"There has always been something I found strange. An existence like you should not have been able to be summoned as a Servant. Then I read Ophelia's records and found a possibility. Her Mystic Eyes can see through the future. So imagine this: at some point, her Mystic Eyes accidentally saw the Lostbelt and saw you. Then everything became possible."
"If my guess is correct, the Servant Ophelia originally intended to summon should have been Sigurd. But you found a loophole and replaced him. No, it would be more accurate to say that you seized Sigurd's