@Baronoflight
@Leonhart93
I legitimately can't tell if this is bait or actual ignorance (I don't mean that in an insulting way, I mean it literally as being uninformed), so if I fell for the joke, that's on me.
Basically, this is an adaptation of the first route, titled "Fate," of Fate/stay night, a visual novel made by TYPE-MOON in 2004 (for reference Fate/Grand Order was first released in 2015, granted, unlike Fate/stay night, Fate/Grand Order actually got an official English release). Fate/stay night, while not the first entry into this expanded TYPE-MOON-verse/Nasuverse multiverse, is probably the most influential as it launched and laid the foundation for the entire Fate series, including Fate/Grand Order. It created the concept of Servants, Masters, the Holy Grail, the Holy Grail War (especially the Fuyuki Holy Grail War), many powerful mage families like the Einzeberns, and many other ideas that would be used in future titles, so it really is important to the rest of the franchise. It was also the first game that TYPE-MOON released as an official company, so it has some symbolic importance as well.
While you may be correct that in the grand scheme of things in the world, Fate/stay night is a much smaller scale story and (along with most Nasuverse stories) have nothing on the scale of the impact of Fate/Grand Order in terms of scale in the world (world-ending apocalypse and universal genocide will do that) and general popularity (10's of millions of players and being (if I remember correctly) the highest-grossing mobile game (let alone TYPE-MOON game) of all-time is nothing to scoff at), it (Fate/stay night) still is important to the world of the story.
Also, Fate/Grand Order is technically a spin-off of Fate/stay night, so that's cool.
Actually, they're set in different universes, so the events of Fate/Grand Order don't happen in the world of Fate/stay night and vice versa. Make of that what you will. Actually, every Fate/Nasuverse work exists in its own universe, but also sometimes exist in the same world/timeline, Pokemon-style (basically, some works exist in the same universe (like Tsukihime and Fate/stay night), but they also exist as separate universes (same example), I think I just overcomplicated things, just ignore this).
(Also, you can see if something is a doujin on Mangadex because it's labeled as one).
TLDR: I may have fallen for a bait and tried (and maybe failed) to sort of explain why Fate/stay night is important despite its much more limited focus compared to Fate/Grand Order. (Also, I really like Grand Order, so if it somehow comes across that I hate it, just know that I don't). If this was helpful, great! If I fell for a bait, that's also kind of funny, I guess. If this didn't make sense, I (or someone else) might be able to clarify some things.