Watching Marvel's what if series I started wondering if some anime series could have this small change that could completely change how everything continues beyond that point (SPOILERS for attack on titan and code geass) like imagine a what if of attack on titan where erwin is given the colossal titan, or lelouch geass not turning on with euphemia on the first season, these things could possibly give the series a completely different ending, just wondering if other people have a what if in some anime and maybe what could that change
-All Fate/stay night routes are a what if. This is the most clear example.
-Fate/Apocrypha:
*After the Holy Grail was stolen from Fuyuki following the third Holy Grail War by the Yggdmillennia, it was no longer held there and was instead held in Transylvania.
*There have been numerous Holy Grail Wars fought all over the world since the theft of the original grail, which is presumably how Waver managed to achieve the title of Lord El-Melloi II as in Fate/Zero. The main difference is that the Romania Leyline is better than most, allowing the summoning of fourteen Servants rather than fewer than seven (a number of these supplementary Grail Wars apparently don't even boast a normal complement) and is capable of reaching the Root.
*And the original summon catalysts for the usual Fate/stay night and Fate/Zero Servants have been lost since, once the information of the war spread, they were stolen and passed around until no one knew where they were. The Servants of Apocrypha can seem a little "second-string" because that's the point - they're easier to summon with broad catalysts (like Mordred) or are a bit obscure and all their relics haven't been plundered yet. However, it is implied that El-Melloi II managed to keep the very same catalyst he used to summon Iskandar in the Holy Grail War he participated in.
*The material book reveals what happened to major characters from Fate/stay night in this timeline: Kirei grew up in an uneasy coexistence with Amakusa as a "stepbrother", and took over the position of priest when Risei died of natural causes. Because there was no Fourth Holy Grail War, he never experienced the development of Zero, though Amakusa is wary enough to avoid him in case that actually does happen; because the Grail was stolen by Darnic, Zouken is completely shut down and the Matou family dies off as a result; the Tohsakas completely give up on the Greater Grail to reach the Root after the Third War, instead becoming Kung Fu Wizards specializing in Chinese kenpou to do so. Tokiomi's dilemma of having two daughters to raise still happens but because the Matous are no more, the Edelfelts adopt Sakura instead. Sakura grows up to be a pro wrestler and becomes Luviagelita/Luvia Edelfelt's tag team partner; the Einzberns just decide to try and create a new Greater Grail from scratch. Kiritsugu is never hired and subsequently Ilyasviel is never born, so the Einzberns will eternally toil since Ilya's nonexistence means there is no ultimate failure to give up on; the Fuyuki Fire never happens so Shirou lives out a normal life with his surname unchanged to "Emiya" and a much more cheerful disposition. Rin and Sakura are still his love interests.
-Fate/Extra
Supposedly, this game takes place in a timeline that diverged from the normal Fate/stay night universe in 1980, when the prana of the world suddenly vanished. According to Rin and Twice, this shouldn't have happened, and history is corrupted somehow. Also, the moon landings haven't taken place yet, despite occurring in the normal timeline before the prana vanished. Leo's dialogue implies the Harway family prevented space-travel to prevent anyone from landing on the Moon.
-Fate/Grand Order
The game itself takes place in a separate timeline from Fate/stay night, because their Fuyuki Holy Grail Wars are very different from the original timeline, like there being only one known Grail War to Chaldea. El-Melloi II's the first one to bring this up during "Fate/Accel Zero Order", because when he looked through Chaldea's records of them, they clashed heavily with what he remembers/the Association's records on them. It's revealed in the Camelot chapter that Olga-Marie's father was the victor of the 2004 Fuyuki Holy Grail War.
--Also, since many of the Servants come from works that are themselves Alternate Timelines, and they can often remember those timelines; it is difficult to differentiate whose history belongs where. Waver and Dr. Roman refers to these differences as "part of the same time cluster" and are "forgivable" by the World.
--The female version of Miyamoto Musashi comes from her own timeline which was implied to be pruned at some point. In addition, the pseudo-singularity she appears in is its own separate timeline, which is plot-critical, as the villains are taking direct advantage of that to interfere with history.
--The Lostbelts are alternate Timelines that have replaced proper history in a certain area on Earth. The years attached to them aren't what time you're going to. It's when the timeline was changed.
-Fate/kaleid liner PRISMA☆ILLYA
Prisma Illya takes place in an alternate version of the Fate/stay night universe where Fate/Zero never happened. 2wei! implies Kiritsugu and Irisviel murdered the other Einzberns and destroyed the Grail ritual in order to protect this version of Illya instead.
All weebs creatures of the galaxy, hear this message. Those of you who listen will not be struck by western animation. You will no longer know hunger, nor pain. Your Anime have come to lead you now. Our strength shall serve as a luminous sun toward which all intelligence may blossom. And the impervious shelter beneath which you will prosper. However, for those who refuse our offer and cling to their western animation ways… For you, there will be great wrath.
