Avenger's True Name is Amakusa Shirou Tokisada (天草 四郎 時貞, Amakusa Shirō Tokisada?), the teenage leader of the Shimabara Rebellion. This version of Amakusa is a traveler from a culled parallel world, much like the female Miyamoto Musashi.
Due to his experiences in numerous parallel worlds, he has despaired of the human condition and his personality greatly differs than his counterpart.
Shimosa Province: The Stage of Rivers of Blood and Mountains of CorpsesEdit
He is the known as the Sorcerer (妖術師, Yōjutsu-shi?). Having traveled several worlds, he eventually had a revelation from a unknown being, who gave him instructions on how he can carry out his revenge against the mankind. At some point, he meets Caster Limbo and together they decided to carry out a plan to exterminate humanity.
Due to a weak Counter Force on the timeline and several requeriments fuilfilled, he choosed Shimousa as the right place to execute his agenda without so much oposition. He and Limbo decided to summon several servants and engrave upon them the Curse of Annihilation, turning them into undead, bloodthirsty monsters, thus creating the Heroic Spirit Swordsmen, whose purpose was to massacre every human life on sight without exception, and using the negative energy of the souls of the victims as fuel to activate the Onri Edo upon the Castle of Toke.
His main goal was the completion of the Onri Edo with the sacrifice of a princess of the Matsudaira clan. According to him, once the ritual is complete, not only that timeline will be engulfed by the darkness, but, like a curse transcending worlds, it will affect every timeline where the Tokugawa clan has left a trace in history, eventually reaching Chaldea and bringing a great calamity to the Time Tree itself. 
His ability and sorcery to summon and corrupt Heroic Spirits stems from a being he calls "Satan."
As an Avenger, Amakusa Shirou possesses the Shimabara Hell, a reality marble that reenacts the hell that he lived in the Shimabara Rebellion in which he was the sole survivor.
- ↑ Fate/Grand Order Epic of Remnant - Shimosa Province: The Stage of Rivers of Blood and Mountains of Corpses, Chapter 15