Is that really anything new with Nasu and his lore consistency at times?
To be fair, if you realized that Earth's civilization can extend to thousand of years into the future, and Heroic Spirits are chosen from those who has accomplished 'legendary' level feats, the definition of 'modern' is ever-increasing. Shooting a revolver gun from 1900s 6 times manually under a second may been a legendary feat compared to when you have a 37650-times per-second firerate laser blaster. Or what if Earth underwent a cataclysmic event where civilization got reset from zero, and weapons became relics? Doesn't it count as legendary weapons heroes wields?
Atop of that, the definition of 'heroism' always differ from age to age. Heck, Shirou became a Heroic Spirit even if he comes from modern age.
Is that really anything new with Nasu and his lore consistency at times?
He's actually consistent about more than people want to admit (because memes and things actually being complex with variables), but many people make the mistake of assuming that the summoning system of Fate/Grand Order operates under the same rules as the one used in Fate/Stay Night. While it can and usually does access the Throne of Heroes, it has additional functions that lets it summon copies of just about any being that has a Saint Graph that has a karmic tie to the summoner (the player character), which is why we can summon so many strange beings regardless of their age of origin or if they are even from human history.
In this case, Koyanskaya was said to be a "shadow of Tamamo" that came from another timeline/world, so she's already old enough to be summoned as a Heroic Spirit under the right conditions, and she specifically chose every action she did over the story to try and make herself a separate type of divinity from the original Ameterasu and attaining Beasthood, in her case actively shooting (heh) for becoming a goddess of mankind's weaponry. She apparently succeeded to a degree, but we probably won't know how until the next major story chapter. Her actions most definitely forged a karmic tie to the protagonist, as well. Old or new, she has a Saint Graph and a karmic tie; after a certain point in their conflict, she was going to end up summonable. In short, she's doing what any clever villain does: bending the rules without breaking them.
He's actually consistent about more than people want to admit (because memes and things actually being complex with variables), but many people make the mistake of assuming that the summoning system of Fate/Grand Order operates under the same rules as the one used in Fate/Stay Night.
Thing is, when your go to excuse is "its not inconsistency, it's a different universe! with different rules!" it doesn't really stand up to the critique because it still is very much a case of him(or other Fate writers) just making up new rules without any real foresight, only to retcon them whenever it became inconvenient.
The franchise would've been so much less convoluted if like 70% the rules aren't these pointless flavor texts that will become obsolete every time they have a new update.
remember when nasu said that modern heroic spirits couldn't exist due to fire arms accessibility and easy of use? Now we have a godess of gun!
If I remember it right, the actual statement is that people from modern times with modern weapons cannot, normally, be summoned as servants. It would be hard because logic, it's harder to become a historical figure, a legend, in modern times. Holding guns with training nowadays is an example.
The modern weapons thing aside though, I believe it's more of a way to rationalize through lore, why they don't do characters based off of modern people due to having people with their IPs, friends and relatives still alive and so on.
