“Our stage will be the Offshore Oil Rig, Seraphix,
now a hellish recreation of the Moon Grail War.
This is a cage of ecstasy from which only one can escape.
Only moments remain until the base disintegrates.
And what is it that lurks at the bottom of this dance of Egos…?”

Chaldea has received a cryptic SOS dispatched from Seraphix, a distant oil drilling platform owned by Chaldea in the Pacific Ocean. What worse, when Chaldea attempt to verify Seraphix’s location with Sheba, the result was negative; it was as though the oil rig’s existence has ceases and they were unable to track the source of the SOS.

That’s when a mysterious A.I. by the name of BB hacked into Chaldea’s system and cheerfully announces that Seraphix has somehow been transported to the distant future of 2030 into the Mariana Trench, where it has been sinking for a while and that she is here to help.

BB then informs that she'll use her hacking skills to allow Chaldea's Rayshifting system to transport the protagonist to the future for this occasion.

Kengoro Nishide of "Umehara FIGHTING GAMERS!" Breathes new life into "FGO"