The hotel's magic is capable of letting two people from worlds with conflicting magical systems interface with each other. It's probably that the dream of the hotel is converting our own natural existences into Ghost Liners, while Ritsuka's conception of us within the dream acts alongside her natural prana to produce a fitting amount of Spiritrons to engage with the Throne of Heroes. Normally, this would probably only produce simple servants from the first Holy Grail War as envisioned, but the magical contract with me allowed the Stellaron temporary access to Akasha, forcing a brief period of time where the system went haywire and several Extra classes were summoned in rapid succession.
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