Bear in mind, that when I say Abyss, I mean the Khaenri'ah-related Abyss that seems to have risen from the ashes of the Eclipse Dynasty's collapse.

From what little concrete information we know about Khaenri'ah's fall and the subsequent Cataclysm, at least three of the Seven Nations under Celestia's "benevolent" eye fell under siege to the creatures pouring out from the Abyss-- which, in of itself, seems to mean quite a few things; what was left of Khaenri'ah, the underworld of Teyvat, a monstrous realm somewhere else... the Abyss is a name for many things.

Regardless, from the Abyss the monsters came, and at some point they invaded Inazuma, resulting in the deaths of Chiyo, the Kitsune Saiguu, Takamine the Mistsplitter, and possibly Makoto (though she probably died in Khaenri'ah). It's Chiyo's death that got me wondering, though-- consumed by a "beast of sin" before cutting her way out, poisoned and corrupted, turned against Ei. That's how she gained the name Tiger-Bite.

I've never heard any mention of an Abyssal Tiger-Demon anywhere else.

Maybe I missed something, or maybe I didn't.

Or maybe, there was no Abyssal Tiger-Demon in the first place.

So, Inazuma borders the Dark Sea-- the lands and oceans beyond what I'm going to call the Known World. When the Archon War ended, the gods who did not submit to the Seven were either killed out of hand, or fled to the Dark Sea, unwilling to bend. What they doo, what they plot or scheme, no one seems to know, though I personally doubt they would simply consign themselves to an eternity away from what was once their domains, awaiting Erosion to end them. Maybe they're waiting for a chance to return.

And what better chance was there in the last few thousand years than the Cataclysm? Two the Seven had died, replaced by Archons that, as far as the Gods of the Dark Sea knew, were inexperienced. What better time to re-emerge from the Dark Sea?

And, considering how many gods Teyvat used to have, is it out of the question that one of them might have been a tiger? Orobashi was a snake, Rex Lapis was a dragon. Why not?

Take that as you will.

^{im probably reaching a bit tho.}

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I'm not sure how to actually end thus rant other than a

TL;DR: the "Abyssal Invasion" of Inazuma was, in fact, an invasion from the Gods of the Dark Sea.