Beginner's Guide to Genshin Lore
In the perpetual meantime of a sheltered eternity, most are content to live, and not to dream. But in the hidden corners where the gods' gaze does not fall, there are those who dream of dreaming. Some say a few are chosen and the rest are dregs, but I say we humans have our humanity. We will defy this world with a power from beyond.
— Dainsleif, Teyvat Chapter Storyline Preview: Travail
The Teyvat we know only comprises a small portion of the waking world. As the Archon War approached its end 2000 years ago, the gods that refused to recognize the rule of the Seven fled to islands across the Dark Sea — towards regions beyond the control of the Seven — becoming 'evil gods'.
<aside> <img src="https://static.wikia.nocookie.net/gensin-impact/images/1/17/Item_Bit_of_Aerosiderite.png/revision/latest/scale-to-width-down/512?cb=20210109215827" alt="https://static.wikia.nocookie.net/gensin-impact/images/1/17/Item_Bit_of_Aerosiderite.png/revision/latest/scale-to-width-down/512?cb=20210109215827" width="40px" /> The coastal nations of Teyvat refer to the region beyond the protection of The Seven as the Dark Sea. It is said many defeated gods refused to live under the new order of The Seven, so they fled to remote islands and became evil gods. However, their powers came from the same source as Rex Lapis, separate from this all-devouring darkness. –– Bit of Aerosiderite
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The ancient nation of Khaenri'ah was destroyed 500 years ago. In We Will Be Reunited, the Traveler reveals that their sibling woke them up in the midst of a sea of flames & destruction — this was the fall of Khaenri'ah. Once glorious, the nation was ruled by the Eclipse Dynasty (Chinese: 古国黑日落 Gǔguó Hēirìluò, "The Ancient Civilization of the Black Sunset") until its own fall led to the cataclysm, the gods bringing chaos across the world.
As a godless nation, Khaenri'ah prospered in power. Built purely by humans as an underground realm, Khaenri'ah reached immense levels of advancement — described as the "pride of humanity" by Dainsleif — until struck down by Celestia for reasons still unknown.
Dainsleif hints towards the destruction and flames that ensued as a result of "mortal arrogation".
With the destruction, many Khaenri'ahn's were cursed and turned into monsters of the Abyss — becoming the lost Hilichurls and mobs we fight today. (While Hilichurls have been present for millennia, Khaenri'ahns were cursed to turn into these 'primitive' creatures.)
On the Eclipse Dynasty
<aside> <img src="https://static.wikia.nocookie.net/gensin-impact/images/4/48/Book_Breeze_Amidst_the_Forest.png/revision/latest/scale-to-width-down/512?cb=20210313022137" alt="https://static.wikia.nocookie.net/gensin-impact/images/4/48/Book_Breeze_Amidst_the_Forest.png/revision/latest/scale-to-width-down/512?cb=20210313022137" width="40px" /> The Eclipse Dynasty had fallen, and disaster spread across the land. The alchemist known as Gold was corrupted by their own greed and ambition, and created an army of shadowy monsters with their uncanny powers. –– Breeze Amidst the Forest
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On Hilichurls
<aside> <img src="https://static.wikia.nocookie.net/gensin-impact/images/9/91/Item_Ominous_Mask.png/revision/latest/scale-to-width-down/512?cb=20210110031519" alt="https://static.wikia.nocookie.net/gensin-impact/images/9/91/Item_Ominous_Mask.png/revision/latest/scale-to-width-down/512?cb=20210110031519" width="40px" /> Since the pitch-black calamity from five hundred years ago, they have begun to spread in large numbers across the land. They are not very strong, and they lack organization, but they nonetheless bring sizable trouble to humans every once in a while. –– Hilichurls, Archive
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Khaenri'ah was an underground realm, and its natural fauna were few indeed. As such, its alchemy focused more heavily on the creation of life. This art of creation was known as "The Art of Khemia."
Advanced combat automatons like Ruin Guards are products of Khaenri'ah, codenamed 'Field Tillers', that now wander towards Teyvat's ruins, masterlessly defending them as they once did Khaenri'ah. Along with this technological prowess, it's implied that the nation was militaristic in approach: "The land is not to be tilled with farming tools, but rather to be fought for with steel and blood," Dainsleif quotes.
Ruin Guards from Khaenri'ah roam all over Teyvat, gradually spreading to every corner of the region. In Stormterror's Lair, an interactive/non-fightable Ruin Guard stares directly towards Celestia.
<aside> <img src="https://static.wikia.nocookie.net/gensin-impact/images/8/86/Enemy_Ruin_Guard_Icon.png/revision/latest/scale-to-width-down/256?cb=20201120070819" alt="https://static.wikia.nocookie.net/gensin-impact/images/8/86/Enemy_Ruin_Guard_Icon.png/revision/latest/scale-to-width-down/256?cb=20201120070819" width="40px" /> "Perhaps resonating with the sorrow of other civilizations across the time, they found their way to various ruins across the land, where they lie dormant." –– Dainsleif, A Herald Without Adherents
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Other Ruin Guards have been inscribed with messages from the long lost nation. In Dragonspine, Ruin Guards demarcated with Serial Numbers reveal a cipher telling of the nation's tragedy. (First post about solved Ruin Guard Cipher)
For the nation we can't forgo this skyborne power, but we failed.