There are a handful of Axis Powers Hetalia fics that picture Nations at either the end of the world or their own "lifetimes." Whether it's peaceful, violent or tragic depends on the writer. But let's just say that they take it well...
Sometimes, this can include the end of a particular era of their history. Such as the French Revolution or the final years of Austria-Hungary.
In canon, England reflects on the loss of the British Empire, and France thinks about Joan of Arc and Napoleon as he's being defeated by Germany in WWII.
The Big O's Paradigm City is a unique example in that the Golden Age was forcibly suppressed and all memories of that time were erased, thereby skipping the long decline. The result is a grungy, post-apocalyptic noir New York City in which the Lost Technology is memories and the occasional Black Box pops up in the form of giant robots, artificial stars, and advanced androids.
Season 1 was quite possibly the last TV anime to be drawn on cels and transferred to film.
Fairy Tail has this with the Tartaros arc. Nearly the entire Magic Council was assassinated, Acnologia kills Igneel, the other dragons are revealed to have already been killed by Acnologia, Zeref destroys Mard Geer permanently and makes off with the Book of E.N.D., the Fairy Tail guild hall, along with a good portion of Magnolia Town, was wrecked in the struggle and Makarov disbands the guild at the end of the arc.
As a fantasy historical story near the end of the Edo period, Hakuouki depicts the end of the age of The Shinsengumi and of the Japanese warrior as Westernization and its advancing weaponry are becoming more prevalent and the characters learn to cope and adapt to it.
Throughout Lone Wolf and Cub, it's both expressed and strongly implied that Feudal Japan is about to come crashing down and that Itto is "the Last True Bushi."
Magical Record Lyrical Nanoha Force shows the start of the end of the magic age for Lyrical Nanoha, with the Eclipse having Anti-Magic strong enough to actually make magic obsolete and force the (re)introduction of physical weapons, unlike StrikerS where the heroines could simply power through it. However, the sheer amount of Fanon Discontinuity raises the question of whether this series will stay canonical, especially given its sudden "hiatus".
My Hero Academia: This is what happens after the climactic battle between All Might and All for One. Although All for One was left defeated and subsequently imprisoned, the battle used up the last remaining "embers" of One for All that allowed All Might to remain a hero. Recognized throughout the world as the Number One Hero and The Symbol of Peace, it was his presence that inspired hope in the populace and served as a warning to villains. With his retirement, villains that had been driven into the shadows start coming out of the woodwork to strike out at a world that has lost its greatest protector. Other heroes have recognized this with the noted rise in crime rates being a sign of everything that All Might built is slowly crumbling down.
In Natsume's Book of Friends, many spirits are departing and/or becoming weaker as less and less humans believe in them. An example is when one shrine god vanishes entirely when his last worshiper dies.
One Piece. Several characters have different views of what exactly this "New Age" brought on with the death of Whitebeard at the end of the War of the Best, confirming the existence of the One Piece and therefore ushering a new wave of pirates to sea is about, mostly thinking of a world in the verge of chaos or an age where pirates no longer chase their dreams. For example, the Marines seem to think of it as an age where pirates are more ruthless than ever, whereas Trafalgar Law thinks of it as an age where the Marines' days are numbered, and X Drake thinking this is a new age for the Marines as well upon Akainu becoming Fleet Admiral and they receiving unprecedented power by the World Government. Eustass Kid seems to hold the belief that pirates are in an Evil Power Vacuum, dog-piling over each other to get at One Piece — not so much about being the Pirate King anymore. Bellamy believes this "New Age" is an age without dreams. Or at least he used to, before coming back post-Time Skip with a change of heart and looking to pursue his own dreams. And Blackbeard? He thinks of it as the age of his own world domination.
Toriko has a chapter aptly named "End of an Age", because Midora causes so much destruction to the Human World that 100 nations are unable to function properly, as the ecosystems are destroyed and, in turn a shortage of ingredients breaks in. Truly the end of the Gourmet Age. In turn, due to this shortage, IGO creates Food Pills to try to apease the hunger, because the only way to get ingredients is to go to Gourmet World.
Sailor Moon states that an unidentified length of time ago, the entire Solar System was ruled in peace by The Moon and its queen, and every planet was a utopia, in an era known as the Silver Millennium. Now, though, every planet but Earth is dead. (Sailor Moon does promise via Time Travel, though, that the future will be bright — and based in Tokyo.)
In Sgt. Frog, a flashback chapter revealed that shortly before Dororo reunited with his platoon mates, the denizens of the ninja village he had been living with (including his friend Koyuki) were forced to re-integrate with normal Japanese society after Japan's "department of ninjutsu" was disbanded.
Holo of Spice and Wolf decides to leave the villagers she helped because they say that they don't need a harvest god anymore. While she initially helped them by making the crops grow, she occasionally had to do the opposite to prevent the growing village from being struck by the Tragedy of the Commons, which made them resent her. In the first episode, before she leaves, we see her portrayed in the village harvest festivities as an oppressive force and a thief instead of as a wise benefactor.
In the original light novels that progress past where the anime ends, this trope is made more explicit as Lawrence and Holo travel further northward towards her home. The old gods of nature that reigned before the rise of humans have been killed or forced to flee their homes by the Moon-Hunting Bear, the survivors quietly blending into human society. Even Holo admits late into the series that her kind's era is fading, though that doesn't mean she can't find a new life with Lawrence.
The aliens of Tokyo Mew Mew see Earth as exactly this due to pollution.
Partially pollution, and partially because these "aliens" are actually the original inhabitants of the planet, and want to know what the hell we humans are doing bumming around in their property.
∀ Gundam has this as its distant backstory. They even have a name for it: The Black History. That backstory happens to be the entire Gundam franchise up to that point; Word of God adds in most later Gundam series to backstory.
Urusei Yatsura had this in the third movie "Remember My Love". When Lum is kidnapped, all of the Oni leave Earth to find her. Eventually the character's lives return to those of normal teenagers; time even becomes unstuck and our characters advanced to 12th Grade. This is all wiped out, and the original timeline restored by the end of the movie.
Yokohama Kaidashi Kikou shows the "age of the calm evening" before "the night of humanity". This is paralleled in Alpha's own development.
In Attack on Titan, the country Marley had previously exerted dominance over most of the world through its use of Titans in warfare for a long time. But now, the rest of the world is developing technology strong enough to combat Titans and even defeat them. So the current priority for Marley is to try to find a way to regain their dominance.
Maquia ends up outliving all the ordinary humans she knew.
The renato dragons in Mezarte kingdom's control are gradually dying out, resulting in its royal family looking for another asset. They settle for kidnapping the women from a Society of Immortals and destroying their homeland, forcing those who have managed to evade both capture and death into parting ways and hiding.
For the ordinary humans appearing in the story, the changes in society as a whole result in children who grew up in farms becoming factory workers and soldiers by the time they are old enough to work.