The bit with Merlin being the Anti-Christ is debatable. Merlin is sometimes depicted as having a Devil or Incubus as a father, though his being baptised seems to be a common trend.
The idea of DxD Vortigern being the original Wielder of Divine Dividing comes from Type-Moon Vortigern, who according to the wiki is said to have taken the power of the White Dragon in contrast to Saber, who was gifted with the aspect of the Red Dragon.
With this, there is now yet another parallel between Shirou's World and the DxD world...with more possibly on the horizon.
"Thanks again for the help, Emiya-san." Saji sighed, the Sitri pawn slumping back against the wall while rotating his shoulder "Kaichou's been running us ragged with preparations for the upcoming conference so having an extra pair of hands to handle open-day really helps out."
"I can imagine." Shirou mused, knowing all-too-well how much of a perfectionist the Student Council President could be, even before discovering her true nature "Is there much more that needs to be done?"
"Not really, we're pretty much set for this evening." Saji sigh in relief "Still, I can't help but envy the ORC," he admitted with a scowl "Especially that damned Issei, lucky pervert hasn't a care in the world."
"I wouldn't go THAT far…" Shirou grimaced, recalling the tense meeting between the two Dragon Emperors. After all, just because Vali had promised to refrain from starting anything didn't mean he'd back down from a challenge, and it just so happened that the White Dragon Emperor had a nasty habit of choosing his words to deliberately get a rise out of people.
Put simply, had Rias not shown up with her brother & Grayfia at that very moment, it was highly likely that Issei's short fuse would've led to him assaulting his 'Destined Rival', thus giving Vali carte blanche to beat his inexperienced ass into the ground, an act which would have dragged in the rest of the Gremory Peerage, and quite possibly the Lucifer himself.
In short, Saji's assessment that Issei had nothing to worry about couldn't have been more incorrect. If anything, the Red Dragon Emperor had more to worry about than any other Devil at Kuoh save for Sona & Rias, given their responsibilities as overseers and the upcoming conference.
"By the way, Emiya…" Saji began hesitantly, snapping the Faker out of his thoughts, only to blink at the look of concern the Sitri Pawn was sending his way "Are you sure you're alright? According to the report Kaichou received, you got messed up pretty bad."
"Ah, I'm all better now." Shirou assured the blonde pawn, surprised and honestly flattered for his concern, no doubt a testament to his close relation with the Student Council "I just pushed myself a little too hard, that's all."
"If you're certain." Saji trailed off, looking unconvinced, only to flinch as the bell rang, signalling the start of the school day "Crap, you'd better get back to Class Emiya, Kaichou will have my head if you wind up tardy because of me."
"Understood, take care, Saji-san." Shirou offered, the two going their separate ways, the redhead jogging lightly towards his classroom, pausing occasionally to greet and assist several adults that had gotten lost on the way to a specific classroom, which was only understandable considering the size of the Academy.
'So this is what Taiga had to go through every year…' he mused, chuckling at the memory of his hapless guardian running around like a headless chicken trying to get everything ready, even as the now familiar ache in his heart kicked up at the reminder that he'd never see her again 'Such a shame Kiritsugu could never make it.'
"Ah! Good morning, Shirou-san!" a familiar voice greeted as he opened the classroom door to be greeted by a smiling Asia Argento, accompanied as ever by a smirking Kiriyū Aika. To this day, Shirou still could not comprehend how the Innocent Devil (and wasn't that an oxymoron?) had befriended what was essentially this world's incarnation of Tohsaka Rin in terms of sass, as he was fairly certain Aika was unaware of the existence of the Moonlit World or Asia's true identity.
"Morning, Asia-san, Aika-san." He greeted, having learnt the hard way that referring to the bespectacled girl by her family name was to invite trouble, only to blink at the sight of a scowling Issei nursing a swollen cheek "What happened to him?"
"Just a couple of parasites showing their true colours." Aika scoffed, earning a glare from Matsuda and Motohama "It's kind of sad how Hyoudo persists in calling them his friends no matter how many times they stab him in the back."
"Shut your mouth, Kiriyū!" Matsuda snapped, the former jock clenching his fist in anger though wisely deciding to remain in his seat in the face of Shirou's warning glare "Issei's the one who betrayed us first! How dare he be so popular with women without sharing the wealth?!"
"That's right, Matsuda-kun!" Motohama preened, adjusting his glasses in what he probably thought was a superior manner but really just made him look a prick "Did we not vow to share everything together? As his brothers in arms it is only natural that we punish him for his transgressions."
"In short, they can't accept the fact that Hyoudo's surrounded by hot babes while they're stuck with their left hands." Aika sneered, causing the two to slump in defeat as a funeral bell chimed overhead "I'd almost pity them…if they weren't so pathetic. Almost as pathetic as what they're packing."