He is the Servant of Flatt Escardos in the Holy Grail War in Snowfield.

He is the embodiment of the mystery behind the legend of Jack the Ripper. Thus he has no true form, and is capable of shapeshifting into any form he desires.

The legend is full of madness, which the Berserker class gives to the Servants in its class. So in an odd twist of fate, this Berserker managed to keep his sanity just because had been summoned as a Berserker and not under another class.

Years after the Fifth Holy Grail War in Japan, strange reports surface of one appearing in America. Attracting new Mages and Servants, the question is raised about the relic’s authenticity. As the city of Snowfield is turned into a bloody battleground, specific details seem wrong. Is it possible someone is manipulating this twisted little play, and if so, does this mean the true Holy Grail exists?
 

(Source: Crunchyroll)
 
Note: Special premiere occurred in Los Angeles at Anime Expo before the Japanese television premiere on July 2, 2023.

In a Holy Grail War, Mages (Masters) and their Heroic Spirits (Servants) fight for the control of the Holy Grail—an omnipotent wish-granting device said to fulfill any desire. Years have passed since the end of the Fifth Holy Grail War in Japan. Now, signs portend the emergence of a new Holy Grail in the western American city of Snowfield. Sure enough, Masters and Servants begin to gather... 

A missing Servant class... 
Impossible Servant summonings... 
A nation shrouded in secrecy... 
And a city created as a battleground. 
 
In the face of such irregularities, the Holy Grail War is twisted and driven into the depth of madness. Let the curtain rise on a masquerade of humans and heroes, made to dance upon the stage of a false Holy Grail. This is a Holy Grail War covered in lies.
 
(Source: Official Site, Aniplex USA, edited)
 
Notes: 
• Special premiere of Episode 1 in its English Dub occurred in Los Angeles at the Fate 20th Anniversary Showcase event and as well through Crunchyroll’s YouTube Channel on November 23, 2024 before the Japanese television premiere. 
• The Japanese advanced premiere occurred during the "Fate New Year's Eve TV Special 2024" on December 31, 2024.

The stage: the city of Snowfield in the western U.S., far from Fuyuki. There, a "false Holy Grail War", quite unlike the original Holy Grail War, unfolds. There were those who had been keeping an eye on the auguries of the Holy Grail in Snowfield. According to an investigation by the Mage's Association, the Holy Grail War system in Snowfield was an imitation of the one in Fuyuki. What's more, the system was incomplete, leading to the exclusion of one of the seven classes and the selection of beings as Servants who ordinarily could not be summoned. It was, verily, a strange fake. As an organ of the U.S. government executes its various plots, the Servants are summoned one after another...

The plot centers around a Grail War faultily copied from the Third Holy Grail War in Fuyuki. After the end of the third Grail War, an organization from the United States that has magi separate from the London based Mage Association as members took data from Fuyuki's Grail War and planned their own ritual. After seventy years, they used the city Snowfield as the Sacred Land for their own Grail War. They were unable to successfully copy every aspect of the ritual, which lead to it acting only as an imitation that has lost the Saber class and allowed for the summoning of strange Servants due to the definition of a "hero" being blurred. 

(Source: Type Moon Wiki)

A gag manga featuring numerous characters from various Type-Moon works in a school setting.
