Hero? I'm just here to borrow power!

The final battle in Shinjuku, a demonic realm beyond human reach, is a clash of endless swords and endless slashes.
Baiye stood before the two Su Nuo.
Colliding with the realm of birth is a subspecies of fantasy materialization, a grand magic called "Underlying Marble" that rewrites reality.
Above the Red Well in Tokyo, Nidhogg, a planetary life form and a black dragon, wields his power called "Annihilation" against humanity.
However, the supreme light released by the White Night ultimately struck the Black Dragon down from the sky.
Because standing before the Black King was a true giant of light.
Chaldea, the organization that ensures the survival of humanity, faces an overwhelming manifestation of human evil. A girl named Fujimaru Ritsuka requests the Counter Force to summon a Heroic Spirit who can stop this great calamity.
The response she received was not from a Grand Servant, but from a man named Byakuya.
In the snowy city of America, during a Holy Grail War where the real and the fake are intertwined, Byakuya speaks to the girl named Ayaka Sajō before him.
"Tell me, am I the Holy Sword Wielder?"
"I suppose so."
During the Holy Grail War, Byakuya produced a ring-shaped energy object of unknown significance.
"You ask me what kind of holy sword this is?"
"Orb Holy Sword".