A children's after story

Aku, the owner of the bookshop, who owned a vast collection of books, helped me go through some that contained information about the prophecy of the demon king's army and the people who would be summoned from another world.

Most of the books merely contained simple mentions of the prophecy. It was clear that most people didn't really care about it or just didn't believe in it.
The people in this world weren't really worried about this "invasion" that had been talked about for thousands of years.
The most complete version of the prophecy was one that had been turned into a children's book, with lots of images and very little text.

Once I began checking the children's book, it became clear that the prophecy was as simplistic as I had heard from Miss Iria. There was nothing new here... except for something unrelated to the prophecy. Apparently, there was a short story that took place after the heroes defeated the demon prince and the demon king. Some of the pages were too old and damaged, but it was still possible to get a general idea of what the pictures represented.
Apparently, some of the heroes wanted to return to their world after defeating the demon king, but they found out that the elders who summoned them couldn't send them back. It wasn't that they didn't have the power; there was a different issue. In order to summon the heroes, the elders used a series of temples to extract mana from the air and channel it toward a summoning platform. If my interpretation of the pictures is correct, the summoning platform could send the heroes back to their world, but it couldn't properly aim at the target world.
It was a simple issue of "coordinates."
Back then, when people started the process of siphoning mana from our world to this one, they had the right "coordinates," but this knowledge was eventually lost or destroyed. It's not clear.
Without the right coordinates, sending the heroes to their world was impossible. Every time they tried, they failed miserably. Some of them were transported into what Aku described as the "outside void" based on the pictures, but it's what we would call "outer space." That's not a good place to be sent to...
In this short after-story, one of the heroes gathered the five remaining heroes. They each took a position around the summoning platform, raised their hands, and, according to the book's pictures, they were engulfed in flames. What was left of them was a pile of ashes and what appeared to be their souls hovering above. Then, these souls somehow crystallized into shining red crystals... and the hero who had gathered them used these five red crystals as part of an inverse summoning ritual to send himself back to his world, consuming the crystals in the process. It seemed as if the red crystals somehow pointed the summoning process in the right direction, giving it the right coordinates so that the last remaining hero could return home.

This must be the worst children's picture book I've ever seen, but if my interpretation is correct, then things were going to get really bad for us.
The bald bastard must be hunting us down, using his fire pillar spell to turn our souls into the crystals he needs to return to Earth.
It's very likely that heroes have been summoned several times in the past, but because the demon army never invaded, these heroes tried to return to Earth, and most of them failed.
The bald bastard must be part of an old group of summoned heroes.
I wonder just how many times heroes have been summoned to this world...

Leonel: Aku, thanks for your help. This book has already provided enough info. Out of curiosity, have you heard anything about a massive fire pillar appearing in nearby towns?

Aku: Not really. I spend too much time in my bookshop. I rarely hear about things that happen out there.

Leonel: I see... well, I still managed to get a lot of info. Coming here was definitely the right decision. I'll go tell the girls everything I found out.

Aku: Next time you come here, make sure those loud creatures stay outside.

I guess she really hates loud noises.

Leonel: Okay, thanks for everything. See you next time!

I went outside, and the girls were sitting on the ground waiting for me. They probably weren't very happy.

Leonel: Girls, sorry for making you wait. But I managed to get some useful info.

Faylinn: What did you find?

Astra: Anything related to the bald person?

I took my time telling them everything I saw in the children's picture book, as well as my own interpretations.

Astra: Hmm, this is a serious problem. If that's how it is, he will probably try to target your classmates.

Faylinn: Wait, he needs five crystals, right?

Leonel: Yes, and he already has one. Which means he is going to kill four more people.

Faylinn: But how can you be sure he only has one?

Leonel: What do you mean?

Faylinn: If he is a person that was summoned from your world, then he was probably summoned with his friends... maybe... do you think he could have killed some of his friends to get those red crystals? Maybe he already had some crystals but just didn't have enough.

Astra: Faylinn has a point. We must assume he has more than one crystal. In any case, Leo, you and your classmates are in danger.

Leonel: I wonder if my dreams were some kind of warning...

I had to tell the girls about every single one of those dreams, including the most recent one.

But right after describing everything in detail, a massive headache struck.
I suddenly felt dizzy.
I knew what was happening.
But this time I wasn't asleep.
I was awake, outdoors, talking to the girls, and yet...