Child Rearing Hero and Children of the Demon King

It’s the nature of Sages to elucidate when doubts arise.
The Sage’s egg that is Aura possesses such qualities.

「…… Say, Iric-kun? How did your Otousan and Okaasan marry?」

The incarnation of death mother and a sickly Demon King father. I can understand the beginning. From the dying Demon King to the fruits of love, the twins.
But, how did they continue associating?
How did the mother in Netherworld deepen her relationship with their father, and how did the twins were born?
Isn’t there a limit to a long distance relationship?

「I don’t know well~」

Iric casually declared. He still seems to be wary of Aura and has not become a single bit attached to her. His twin Ilya was the same way.

「Both Ilya and Iric felt your Okaasan’s presence, have you not? Do you remember about your Okaasan?」

I was also curious. About the woman who married that Demon King.
What I am curious about the most is why did she leave her children behind. Since the children weren’t living in the Netherworld but in this world instead, it means that their mother visited this world as well.
Leaving such cute children to fend for themselves, why did she leave?

「I don’t remember much~ But, I love Kaa~chan. She smelled nice. Tou~chan stunk of sweat」
「I do not remember much about her. But, I love Okaa~san. I feel warmth from her. Otou~sama always had a fever, so he was cold」

…… Misfortunes never come singly, Demon King.

「He always had a fever? That Demon King…… just how feeble was he…… he did well becoming the Demon King like that……」

Dreaming of the world conquest and harem even though he was constantly suffering from illness. What an idiot.

「Err…… ah~ Pochi」

It was difficult to ask the children, so I called Pochi.

「Nu. What is it Hero? If you want to ask something of me, turn around three times」

He got blasted. Waiting approximately five seconds for Pochi to fall down, I brought my face closer to his. I will scold Iric later.

「You, do you know why the mother of the twins left them behind?」
「Nugagugu…… their mother……? Use your head a little, Hero. Their mother is the incarnation of death. There’s no way she could stay absent from the Netherworld very often」
「Still…… she didn’t have to leave them to the weak and ill Demon King that could die at any moment」
「You are quite heartless for no reason, bastard」
「Ilya-chan, weren’t you lonely?」
「Not at all. I am not lonely because Iric is here. I played by bullying creatures like Pochi when I was bored」
「…… Iric-kun, what about you?」
「Not really. Ilya’s here. I was bullying monsters like Pochi when I was bored, so I was fine!」
「…… Even though they are such cute children, I wonder why…… why my maternal instincts aren’t tickled even a single bit…… as expected of the Demon King’s children」

Aura muttered with a distant look.