Wtf did I just read?? Is it incest or not? Bcs some say its not incest but why did it look...

I think they r not really siblings?

It’s not incest ML is the Devil’s Child and FL is Human but both of them don’t know that they’re not blood related yet.

Honestly, I feel like I've written this 10 times for different people in this CS.
Anyways, I prefer to look at the reasons for both opinions and choose the one I agree with more. On the one hand:
They came out and were formed from the same womb
They were raised as brother and sister
They look exactly the same when human
And most importantly, they themselves recognise each other as siblings.

But on the other hand:
They are technically not the same species
He was born through magical means and not biological
And they were not formed from the same sperm
In my opinion these are enough for me to consider it twincest, so just choose which side you believe holds more significance.
If the circumstances of their birth confuse you then allow me to give you an example of a similar situation: Imagine a young girl born from a husband and wife, a normal human girl, but one day her mother gives birth to a son that was born from the sperm of a vampire and not her husband, so she gives birth to a half vampire that has similar facial features to the members of their family. Now let's say that those two children were raised together by the husband and wife, and they grew up as brother and sister. If they one day slept with each other, would you consider it to be incest between half siblings? If you do, then you can relate it to this situation and say that this is also incest between half siblings. And if you don't, then I guess you can say that this is also not incest.
In the end of the day we enjoy the storyline regardless of how messed up it looks, and we ship Annette with Johan. It's gross, but alas it's just a webtoon.
If you ship it just ship it, you don't need to justify their relationship.

Well said my friend,
Well said.

Well said my friend,
Well said.

Okay thank you for the explaination, for me this is incest bcs they have the same mother. But I will keep reading, maybe at same point this manhwa will make sense to me.