In this world my sister and I are the first Human

'Ah! My head! It hurts!'

"Onii-chan! Are you okay?"

'Huh!? Shina? What are you doing here? And where am I? I remember I was playing basketball at school with my friends.'

"Me too, Onii-chan. I was at home helping Mom with the housework but then my head hurt and the next thing I remember I was here in front of you, Onii-chan."

'What happened to us?'

"Onii-chan! Look around!"

'What! what's wrong? What the-'

Because I was panicking I didn't notice it before but now that I see it. Where are we? Are we in a different world?

What we saw was a big tree standing far away. But the tree was so big that it reached the sky like those world trees shown in the isekai manga I used to read. 

The area we are standing around is a grassland.

----------

'Shit! Shina, don't be shocked. Looks like we are in a different world than Earth.'

"What! Really! Wow so is it like the isekai manga. Were we transported to another world?! Wow! Awesome!"

'What! What's with the reaction?!' It is a different reaction than I expected. I thought she would start crying and such.

"What? What's wrong?" She asks me so innocently that I don't know what to say. Sigh, even though she is my twin sister I don't know what's goes by her head.

'And didn't you hate me reading manga? When did you start reading the manga too?' 

"Well, I... I start reading manga even before you."

'What! Then why did you give me cold looks when I read the manga?'

"It's j-just I didn't want you to know that I read the manga too. I have a pride you know, H-Hmph."

'What! It's so unfair.'

"Hmph."

[You two really are twins! To think you two are arguing in a situation like this. And that too in such a trivial topic.]

"Ah! W-Who is t-talking?"

'W-What! I don't see anyone here?! W-Who is this? Come f-face to face If you dare.' 

[Really! Here I am. Let's see if you dare.]

Like a sci-fi movie, a blue interference with a smiley face appears.

'W-What! What is this?! What are you?'

"Wait, Baka Onii-chan. It's a system. Did you forget you read it in the manga?"

'Ah, Hahaha...Of course, I remember I was acting to scare you. Haha...'

"So, You are a system, aren't you?"

[Yes, I am. I am the mightiest system created by god, Systa. And I am your guide in this world. Hmph.]

'Oh, really. Do you know why we are here then?'

[Of course, I know.]

"What! Why are we here? And it's a different world isn't it, Systa?"

[Yes, you are right. It's a different world than yours and you were brought here by the god of this world.]

'Why? Why did god bring us here?'

"Yes, why did he do that?"

[Of you two were chosen by the god to accomplish a great task for the greater good of this world.]

"What! Don't tell me we must defeat the demon king and bring peace to this world?"

'Or to make this world prosper with our earth's knowledge and technology?'

"Or both?"

[Come on, calm down. Don't get so excited you otakus. God didn't bring you here to do those small things. God brought you here to do bigger things than that.] 

'And what are those big tasks you are talking about?'

"Yeah, tells us fast."

[The god brought you here to...]

"To..."

'To what?' 

The face emoji on the screen hesitates and blushes.

[To make many children and make this world populated with humans/ your children.] 

"What!..."

'What!'

------------

After claiming down,

"What do you mean? Can you tell us?"

[The world you were transported to is named Mystica. This world has many types of animals, trees, and beings. But the thing is this world has no humans on it. So, god has brought you two here so you can solve this problem.]

'So, you are telling me this world has human beings in it, right?'

[Yes.]

"If so, why doesn't the god just create more humans?"

[Well, God can't do it.] 

'Why can't the god do it?'

[Because the god has no more powers left to create humans after creating this world. After creating this world the god spent all his power to create me and transport you two to this world.]

"Hmm, so that's what happened, huh..."

'Then what should we do now? We don't really have any solution to this problem.'

[No, you have.]

'And what is it?'

[You two should have sex and give birth to babies.]

'What! But we are brother and sister you know.'

"What! We have to do incest sex and give birth to babies like those hentai mangas!"

'Wait, what are you talking about Shina? How do you know about hentai manga!? Don't tell me you read those too!'

She blushes and looks elsewhere.

"W-Well...I found those in your room and I got curious about what those were. So, I-I read them."

'What! H-How many did you read?'

"W-Well..."

Her becomes red like a tomato.

'Don't tell me you read them all!?'

"Y-Yes..." She whispers immediately. 

My face becomes red with shame. To think my twin sister read all my hentai mangas related to my fetish. Now she knows all my immoral fetish. Eh, What should I do now? How can I face her now?

Awkward silence...

'So...'

"Hm..."

'If you know all my immoral fetish why didn't you tell it to other? Like mom, dad, or police. Well, think about it if a normal sister learns about or sees her brother's all-immoral fetish, shouldn't she first go to her parent or to the police.'

Why will she go to the police for some fetish you say? Well, I do have some immoral fetishes that are socially wrong and can be asserted for. Like Lolicon and such.

"T-That because... I have those f-fetishes too."

[Wow! Even though you two are twins with the same appearance, I didn't think you two have the same tastes in sexual preference either! Looks like you two are made for each other.]

"Made for..."

'Each other...'

We look at each other.

Our hearts beat watching each other. With love different from familiar love, we look at each other like lovers. 

'Shina...'

"Onii-chan..."