An 18 year old man has chosen to become the Demon King of Greed.
There is a reason why it was specifically fate who forced the 18 year old man to become the Demon King of Greed. They wanted the reader to become the Demon King not the regressor.
The reader never wanted his beloved regressor to die right in front of him. He grew up with the regressor. The reason why fate has purposefully chosen the reader and not the regressor was because no one can fight against Fate.
"You saved me once before"
This time the reader tells him he will repay the debt, he won't allow the regressor to be killed in front of him. He wants the regressor to keep on living in this worldline.
The stone of becoming the Demon King was interested in the 18 year old man. The stone wants to know what will indeed happen if an 18 year old reader becomes the Demon King for his teammates to kill.
All of this was simply to create a new type of story that is very unique.
A fallen star is a demon king. They used to be from above the sky but they have descended below and will do so if they become a demon king.
How can the teammates of the readers' watch them defeat the Demon King when it involved literal stabbing and dying? What is the 18 year old reader trying to do is what the teammates have wondered.
Considering the 18 year old reader who knew so much, he was able to manipulate his teammates to do exactly what he wants. Even if his teammates didn't exactly want it, they just had to do as what the situation of reality told them to do.
The first one who understood the 18 year old reader was the writer. The second one who understood the 18 year old reader was his co-worker. The shield was successfully manipulated to join the fight. The duo of armed forces has agreed to join the fight.
The sword was hestiant at first but she eventually joined in trying to empathize with the 18 year old man. The God of the Sword didn't want to see the 18 year old man die but she still agreed regardless to it anyways.
There were some Indian Gods who wanted the Demon King of Greed to suffer and feel actual pain for once. These Indian Gods thought he deserved to suffer.
The daughter of the 18 year old Reader saw the suffering of her father. He was in actual pain and seemed like he might be close to fainting. The daughter hated to see him suffering.
The regressor who looked at the reader and bit his lip. He didn't want to see the reader like this yet the reader was able to overcome and subdue the regressor. Perhaps the regressor sometimes wondered why the reader would purposefully chose to be the demon king himself.
The 18 year old man gave his daughter and had her use a skill to boost the teammate's power on purpose.
The 18 year old man gives salvation in a very cruel way. He does it in a way that makes you not want to do it. Yet he will do it by making it a story and having people to watch it.