It began with an explosion. In this timeline, the Magus Killer's explosives, intended to merely cause a 'bump' in Fuyuki's leyline, worked better than expected and cut the leyline off from the Great Grail entirely. The Grail system was cut off from its mana source early enough that it still lacked the power to sustain seven Heroic Spirits, despite the leftover energy from the Fourth Grail War. The spirit of All the World's Evil within the Grail raged at this unexpected turn of events and desperately sought a way to conduct a fifth Heaven's Feel and emerge from the Grail.
Were it not for a stroke of fortune, this would have been the end of the Heaven's Feel ritual. But in this timeline, Yggdrasil's degradation had advanced to the point that the Digital World's stability fluctuated nine years ahead of time, and portals began to open in the real world. A different group of Tamers managed to end the threat without revealing the Digital World to humanity, but the damage had already been done. During the incident, a portal had opened beneath Mount Enzo, in the very chamber of the Great Grail. Angra Mainyu took notice, and through the portal, managed to establish a connection to the Digital World's mainframe. There, he found a system disturbingly similar to the will of humanity's Throne of Heroes. Heroes of the Digital World, from every conceivable era and timeline, had their data saved onto the system, memorialized for eternity. With the Great Grail's direct connection to this system, summoning Digimon heroes became far more mana-efficient than summoning human heroes from the Throne.
And so the Fifth Grail War began on schedule, but none of the potential Masters could ever predict the Servant they were about to call forth...
Tohsaka Mansion, Fuyuki City
Silver and iron to the origin. Gem and the archduke of contracts to the cornerstone. The ancestor is my great master Schweinorg.
The alighted wind becomes a wall. The gates in the four directions close, coming from the crown, the three-forked road that leads to the kingdom circulate.
Shut (fill). Shut (fill). Shut (fill). Shut (fill). Shut (fill).
Repeat every five times.
Simply, shatter once filled.
Your self is under me, my fate(doom) is in your sword.
In accordance with the resort of the Holy Grail, if you abide by this feeling, this reason, then answer.
Here is my oath. I am the one who becomes all the good of the world of the dead, I am the one who lays out all the evil of the world of the dead.You, seven heavens clad in three words of power, arrive from the ring of deterrence, O keeper of the balance ―――！
In this timeline, Rin had remembered to set her clocks correctly, and so the summoning ritual was performed at the peak of her power. She had planned to summon her chosen Servant, Saber, but ultimately, the Grail was the one who decided the hero that each Master received and what class they were to be set in. Angra Mainyu took notice of the magus's potential, as well as the Saber that he had planned on inserting into the war, and decided that between Rin's talent and power and Saber's pure might, the war would be too easy for her.
An Archer was sent to be Rin Tohsaka's Servant, and he materialized within the perfectly-drawn summoning circle, kneeling at his summoner's feet.
"Servant Archer. Upon your summoning, I have come. I ask of you, are you my Master?"
Rin Tohsaka, heir to the Tohsaka magecraft and Second Owner of Fuyuki City, had expected some sort of mighty swordsman to be summoned. What she received was in the wrong class entirely, but managed to look absurd, yet imposing at the same time. A bipedal draconic beast clad in black armor with...was that a cannon on his arm?! What the hell kind of Archer was this?
Then, the young magus realized that her summoned Heroic Spirit was still waiting for the contract to be completed, and replied in the affirmative.
"Yes. I am your Master." Rin nodded, crossing her arms. "Now, what's your name and legend? Are you even human?"
"Hmph. If this was anything like the past Grail Wars, you would be a fool to ask. But in this case, every Servant would no doubt be too distinctive to conceal their identity. My name is Imperialdramon, and I am not human. I am a Digimon."
"What the hell is that?!"
With the summoning complete, Archer would have stood up, but the chamber was only just large enough for him to kneel in, and standing would have destroyed the basement. Still taking in the flood of knowledge that the Holy Grail was providing him, he nonetheless scowled in distaste at the thought of having to be bound to a mere human. But the promise of a wish was too tempting, and he would endure this until he found an opportunity to be free of her and forge his own path to victory.