I don't think there is any foreshadowing involved. The Horror/Tragedy/Drama is already long running, ever since the beginning of the story.

The whole point of this story is the warped perspective of the human called existence. Truth is, in logical terms, the definition of existence.
However, what we as humans perceive as "true" and "real" are just shadows cast by their true existence.
This is because of relativity, which says that energy equals mass times the speed of light squared.
This means matter is just energy, and the human senses are unable to detect most of the energy around us,
meaning we're also basically blind to anything that does not manifest as matter, yet still exists as energy, which is the same.

This led us to be wary of "supernatural" phenomenons (which are of course natural, but we are unable to detect them),
making distinctions based on outcome (e.g. ghosts, gods, demons, miracles, spirits, ether, natural energy,etc.) as we are even unable to grasp the shadow fully that is cast upon us.

Since this story plays with the whole inhuman sphere (ghost/god/demon/spirit/whatever) and how it is fitting together (i.e. in the reality of existence, warped by the human perception) as well as the theme of possessiveness,
there are three ways that can play into the existential theme:

1. The denial of your own (separate) existence
This is a common theme across literature and psychological problems, with one party denying their own existence separately to someone elses, meaning that they cannot exist apart. This can be due to reliance on the other party or possessiveness.

In extreme cases, the person denying itself can either fuse with the person in question or sacrifice its life for the other person (the "live on in your heart" trope)

2. The denial of the others (separate) existence
This is the exact opposite to the previous case, usually depicted by someone being extremely possessive of someone else,
sometimes to the point that they follow their every step (stalker) and/or hindering their social interactions with others (if done violently, we get the usual Yandere/Yangire character)

In extreme cases, the person denying the others existence can force them to (partially) fuse with them (in spirit/and or body) or to turn them into a possession of theirs by killing them (and sometimes consuming them)

3. The denial of every other existence
This is the famous "being in their own world"-trope which ignores to a certain grade the existences of others interfering with them.

In extreme cases, this can lead to either seclusion from them world they live in into a void or to the complete annihilation and/or rebuilding of the world you live in (e.g. NGE: End of Evangelion, where Shinji denies the existence of every other human except for Asuka, which leads to the death of all of humanity and a new start of the world with only the two of them).

Funnily enough, Mirai Nikki does a brilliant job of exploring all 3 forms of existantial crisis'/denials, with Yuno first denying her own existence, murdering herself and wanting to make Yukiteru the new god, then denying Yukiterus existence when she fails her initial plan and trying to start over by killing him and becoming god again, and in the end the denial of every other existence except of Yukiteru and Yuno when Yukiteru becomes the new god and holes up for thousands of years in a separate world of void, in which he stares at his phone displaying the last message from Yuno prior to her death.

Since we have already grasped quite a bit of how they interact with others and how they view themselves,
it's highly likely that we will see one of two scenarios:

1. the two gods/demons slowly consume the spirit/life force of their respective others/targets to fuse them with their existence, leading to the decision of the two humans between denying their existence to save themselves or offering themselves up to become part of them
This would be the bad end.
2. the denial of every other existence, meaning the "eternal" seclusion of Yuu and Chiyo from the world that denies them coexistence
This would be the good end.

In both cases, the acceptance of an existence outside of the realm of human perception is coupled with the loss of something, and bound to a decision of what is more important or better said, more true to the main character, because we are not talking about pure feelings but to accept a whole new reality and life within it.

Depending on the possible twists and implications, this could be even more interesting considering the fight of the human mind against insanity during adaptation to the new circumstances, which shouldn't be easy for the main character.

@SweetJelly I posted that the day I started reading this on this particular website. Did you forget the concept of time or something? Not everyone starts reading a manga at the same time lmao

Spoiler@Mathias don’t worry the author said that that the hentai that this is based off of is cannon and takes place after the events of this manga, but at the same time I’ve yet to see any of the other characters besides Chiyo and Yuu in the H version, so maybe the cryptic foreshadowing is for the other characters

@EternalAdventurer This foreshadowing has been happening since the start. How are you just arriving to that conclusion?

@CGO39 One of my favourite ones of all time, Excel Saga, had some characters first appear in a pr0n that the author did earlier. Search for "bleached underpants" on TVTropes and see if there's anything you like there.

The foreshadowing has me thinking no drama tag is going to be a lie sooner or later

The Horror and Drama tag seem apropriate. Im getting a really bad vibe from the way the chapter endings are phrased. Like a deadly vibe.

Also the last pages of chapter 19 and the beginning of chapter 20, something is really of about his background.

Son. What? This series is fucking lit. They need to stop with the deadly foreshadowing tho 😰

The last words from ch.27...oh dear it's going to be bad right?

Chapter 27:

The quarrel they had this afternoon seems to have turned into a scene of friendship.
What happened this time?
sankyuu
Listen, Yuu-kun! It's horrible!

Well, // the Great Goddess over here keeps going on about how she can supposedly go shop for groceries on her own.
All I did was reassure her that she doesn't need to pretend like that.
I see, that's what it was…
TV: First errand special
I'm not pretending! I really can do at least that much!
I told you, it's fine! Don't be so stubborn!
Well if you keep saying that…
I'll show you my true strength!
"True strength"…?

Got it? There aren't going to be any problems, so you two just wait here.
Don't even think of coming with me.
It's all good and well that we're worried… but I do think you should go back… // She'll get angry again if she catches you, you know?
Do you really think I'll let a rare event such as this pass me by?

But she did say she had lived as a human before, didn't she?
Ohhh! Well, about that… // I think that's from the era where people used gemstones as currency.
I, I see…
Welcome~!
…Ah

Three croquets, three fried mackerels,
and also one potato salad, please.
Coming right up!
She's being so polite!
Hohooo…
That'll be 1080 yen, please!

Oh? It seems like she somehow managed to clear this normally! // How boring…
Thank you for waiting! Here are your things.
Thank you very much.
Come to think if it, whose child are you, miss? // I don't recall a beauty such as you being around here…

I haven't seen you in the neighbourhood council gatherings, have I? // Oh, it seems the OO's grand-daughter has come, so is that you?
Or maybe you're the new bride of the XXs, near the river.
But if that were the case, I'd have met you in the memorial of ΔΔ's grampa. // So you have to have come here recently.
There's no way I'd have forgot meeting a beauty such as you, either!
And as for the nephew who came a while ago to the Hasunumas, I'm sure he was an only child… // How queer…

I'm off to…!
Wait!

Please consider this.
Or, rather,
Me being here is, above all,
a completely normal and worthless thing to think about.

Oh, that's right! I'm very sorry about this.
Was that… alright just now…
Well, it was at least the most peaceful conceivable resolution, comparatively…

Thank you very much!
…Get out of there, you two.
So you noticed?
You didn't even bother to hide.
Well, sorry.
…What? // I was just teasing you like always.

You wouldn't be satisfied with just one shopping trip, anyway.
Oh no, I'll fully acknowledge you for today.
For an eternal goddess's first errand, it was a splendid result!
Erm, // if I may…

Me too… It might be a weird thing to say, but…
Doing the shopping properly, // and perservering, // was wonderful, I think.
Yuu-kun…!
Fried food received successfully! (<- unsure about this)
Ah, get back here!

We might not be a family related by blood, but we definitely don't look like strangers either.
Although this relationship is rather weird,
"Those days are so nice,"
is what I absent-mindedly thought then.

I'm curious now. Are there any other mangas adapted from a hentai?

So the thing he cares about most she is going to take is going to be her isn't it...

What kind of awful shit would happen to a normal human that drank Chiyo's milk?

Everytime a new chapter gets uploaded im afraid something bad will happen...

god I wish that were me getting milked by an eldritch abomination

@NaniTheFuck
Spoiler

Is it me or this Manga feels like some Hentai that i read back then...
hmm... i think i have read that hentai.. but i forgot its name

Vitriolic best buds then.

I recommend reading H version too 10/10

@SidLeya Chiyo is not "an onee-chan version of" Shub-Niggurath. Chigo is Shub-Niggurath.

Anyway, here is the script for the next chapter, the 26th one. Anyone may use it for any reason what-so-ever. Raws at https://twitter.com/anenarumono. Please excuse any mistakes I might have made.

Let's go play!
My, you're melting from the heat so nicely, aren't you?
Haru-san, you look so cheerful.
She's like a grade-schooler...
Stop appearing as if it's natural.
I'm sorry, but we have no obligation to accompany you. Do as you will, on your own.

Water pistols?
How about a match?
The prize will be, let's see...
The privilege to sleep one noon in the same bed as Yuu-kun!

What are the victory conditions?
You could just not have bothered doing this...

Of course, it's a death-match! Until the loser collapses.
...I hope you don't regret this.
OK then,
now usually...

Hey wait, that's too sudden!
Normally here you'd confine yourself to within the limits of a human body's ability!
I do not recall an explanation like this.

Have it your way!

Ooh, how scary! You really hold nothing back.
You mustn't do these in human society,
Chiyo-oneechan.

What did you just...?
This is definitely not water.
It's a much much more disgusting, bubbling something...

Yuu-kun is the only one allowed to call me that.
oh shi---
Ahhhhh!

Don't play dead like this, hurry up and change your clothes.
We have to go eat food soon.
Hiyashi-chuuka, then!
Don't be so self-serving.
They got so violent, but nothing broke and no-one was hurt.

You're so kind,
both of you.
Yuu-kun, come on, I'll make lunch!
Hurry, hurry!
Alri~ght!