It's a new addition to the Fate franchise. They recently aired the prequel movie for the show last July 2023 called Fate/strange Fake: Whispers of Dawn. I'm waiting for the anime release as one of the highlight for this years shows.
Note: There are no spoilers under this post. It's just a post introducing the story for those unfamiliar with the franchise. This isn't a movie review. The Fate franchise is a tricky subject to introduce because it has a multiverse element. Think of it as Marvel's Avengers on multiple timelines that each version is just as canon as the others.
Below is a copy pasted plot taken from Wiki about the movie "Fate/strange Fake: Whispers of Dawn". If this is your first introduction to franchise and are interested in the iceberg, I suggest you start with this recommendation of what shows to watch in order. And even if you managed to finish them all, there's still bonus canon stories not explored within these shows as the Fate universe, aka Nasuverse, also has more to offer from other sources materials like the light novels and game. It's not an understatement that this series is a rabbit hole on its own but it's fun.
If ever you see any promotional videos, game or shows about the Fate anime, it's likely that you're only seeing one version of the many alternate realities their multiverse has to offer. You can see the same characters but they'll still be different from another show that features them.
It's been around 4 years since the hype for this was created and I can't believe time passed that fast.
Whispers of Dawn Plot:
The story 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 led 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. - Wiki
The Recurring Plot that ties the Fate Multiverse:
Almost every show will have the plot below as a baseline and adding some twist of the rules.
The Holy Grail is a battle royale between 7 servants and their respective master. It's a ritual made to grant the solo victor's wish. Servants are summoned familiars by mages from the Throne of Heroes who fight for the grail. These aren't real heroes but are exact replicas of the heroes copied from a place that exists beyond space and time.
The 7 servants summoned will be represented by their class categories such as Saber, Archer, Lancer, Rider, Caster, Assassin and Berserker. Think of it as rock, paper, scissors as one class counters the other class. Heroes summoned can range from anyone who fit the class based on the legend they were known for like King Arthur being a Saber because his legend is about wielding the sword Excalibur.
The grail war selects mages that it acknowledges worthy to participate in the ritual but there are cases when random masters who have no affinity for magic get chosen as masters. The battle royale is a prerequisite to activate the greater grail by using the fallen challengers as a sacrifice. This ritual was designed for mages to reach the Root. Reaching the root is the reason for being for most mages, it's the place where the origin of everything that's anything came to be, the ultimate source of knowledge.
This is the bare backbone of any plot related to Fate franchise because the entire drama is centered around how the Grail Wars have influence character lives and the history of Human Order.
Whenever you start a series within the Fate multiverse, just assume that everything is canon because the stories happen in alternate realities where sometimes the characters you cheered for had no happy ending.
Thanks for your time.