If Teyvat is a planet, then what exactly is the 'border'?

Teyvat has its own laws

The border is likely the firmament that surrounds the planet like an eggshell. It is large enough to have enough space for a planet and its moon, as we've seen a moon being dragged through the Firmament. We can only assume that Alice is in charge of the outside of the Firmament while the Shades are the ones handling the inside.

The one that Dottore and Mavuika broke before.

Metaphorical border, I'm guessing. Like Stephen Strange protecting the vicinity of Earth.

what i understand is:

the world have three realm (or dimensions), light, void and human realm. the false sky is just protecting invasion in the human realm.

the human realm is teyvat itself, the light realm is where elemental beings, vishap, and dragon come from? and void realm is where abyss exists.

(its also possible that abyss power originated from beyond false sky, but then hide itself in void realm since the power of elemental and abyss opposes each other)

there is border between the three realm, that what alice is protecting.

just like how durin use his abyss power to interact with hyperborean memory, dottore also do the same to learn about lunar secret, at probably much larger scale. that why alice said dottore has cause problem at border (probably between human and void realm).

edit/tldr: maybe easier to understand if i said the planet have 3 dimensions. false sky protect the planet from alien invasion. the border regulate the interaction between the 3 dimensions.

edit/tldr: when abyss invade natlan, the enemies come from void realm (not paratrooper from false sky). when traveler train with skirk, we just go to void realm (not beyond false sky). 

since skirk is using abyss power, maybe she feel uncomfortable / restricted in human realm? that why alice give her permission to go back and forth to void realm.

it's between Natlan and Mondstadt.

Teyvat is a continent, and once again we're truly never beating the allegations.

It's the fuzzy bits around the edge.

The false sky is the border.

It's probably the same as Earth. We consider Earth and Moon as one enity, because they can't exist without each other.
So Teyvat + 3 (now 1) Moons = Border

The border is the firmament. Nicole implied as much.

Ah yes fuck spoiler tags i guess

I think it's probably a dimensional thing - like the Abyss is trying to get in from another reality outside.

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Border is the atmosphere you silly

Jokes aside it is covering the atmosphere but there are some weak points. For more visual, border is a baloon. If you are carefull enough and strong enough you can enter the baloon without damaging it ( Needle test ).

Teyvat is like an onion. It has layers.

*Ikenai Borderline*

Teyvat is a continent on this planet; we only see Teyvat because Hoyo didn't make the other continents, and it looks better to have Teyvat as a large image rather than a small thing surrounded by emptiness or empty spaces.

We don't even know the border of the earth's atmosphere. Instead, we kind of arbitrarily chose the altitude 100km above the mean sea level to be the Karman line, seperating the Earth and space.

The border is the part where Paimon says explore the area ahead of us later

I suppose its a layer beyond the moon because the false sky streteches beyond the moon and ends witha few stars

The moon and teyvat "planet" is still inside the false sky

There are 2 actually. The false sky and the dark sea.

I read somewhere that people in sumeru thinks that teyvat is flat , so I think there is dome covering the continent because the rest of the planet already got infected with abyss

The barrier of the false sky that surrounds the planet like a Dyson sphere.

A1

Teyvat is a world with no boundaries, we need to create a group to promote this, what can possibly go wrong?

Either the false sky or maybe even the border to the Dark Sea. (I think probably the false sky).

The fake sky, the dome.

The skies?

It’s probably a solar system level barrier

Interplanetary or interuniversal borders id say

Imma be real: I think Teyvat itself is fake. My biggest evidence to this is the existence of Irminsul. The ability to manipulate the memories of everybody in Teyvat (with a very small handful of exceptions) just doesn’t make sense, unless the planet itself isn’t real and is just a simulation. If that were the case then making a change to the root files would alter what everyone remembered. Additionally the fact that Scaramouche’s body can be used as an extremely powerful computer even further pushes the idea of Irminsul being a computer.

Additionally there’s another little tidbit for anyone out there who also plays Honkai: Star Rail. In the Natlan weekly boss fight one of the death lines is “This world… is but… a lie…” You know who also says something similar? The Flame Reaver.

For all the people saying the firmament, I’m curious about the in-game description for the Overflowing Abyssal Power in Nod Krai.

The description:
“Due to its proximity to the ‘border’ of the world, ominous and unpredictable forces see through the Abyssal rifts and spill forth onto the land of Nod Krai.”

If the border itself referring to is the False Sky, how could Nod Krai be closer to it than any other part of Teyvat? It’s a planet and the border is a sphere around it. The way it was described here made me think it was the border between the human realm and the void realm, which could also make sense for the witches defending. We know Dottore messed around with the border to distract them, and in Luna III we saw him influence abyssal mirages in order to learn about the moons.

However if someone has an explanation for why Nod Krai should be any closer to the firmament I’d love to hear it

All three Hoyo games are connected
I am pretty sure they are in same universe we can't proveeit yet that's all.