Matou Zouken, originally named Marisbury Zolgen.
He was of European descent.
His genes also carried the bloodline of the Eighth Pillar Demon God Bael, so beloved by Masters everywhere. Just like his ancestor, he had the same knack for making people want to chop him up!
He had once developed the Greater Grail alongside Winter Saintess Juste and Tohsaka Nagato, the founder of the Tohsaka Family. Incidentally, the Command Spells that had screwed over countless Lancers were also his creation.
The Matou Zouken of old had been an Ally of Justice like Kiritsugu. His reason for developing the Greater Grail had merely been to save all humanity...
Well, good thing he had not succeeded. Otherwise, he might have ended up walking Amakusa Shirou Tokisada's path.
But no matter how great a man he had once been, Matou Zouken was now nothing more than an Old Worm barely clinging to life.
He had abandoned the Matou Family's Magic Crest, abandoned his own body, and abandoned his former ideals. To seize other people's bodies and continue living, he would stop at nothing!
Yes, the old man named Matou Zouken had long lost his former glory. He had become a rotten bug, living only for the sake of living.
"Trash is trash. I did nothing at all, yet merely approaching me made your soul collapse?"
Shirou took a step forward, just an ordinary step forward. There were no special effects, only that terrifying pressure constantly proving how frightening the boy was.
With a pop, Matou Zouken transformed into a pile of worms. The worms clumsily tried to reassemble into human form again and again, but always failed at the very end.
"Can't we talk like this?"
Shirou drew back his aura slightly. There were some things he had to make clear to the