The Ultimate Demon

People sell their flexible souls in exchange for demonic power. Then what does the devil need the soul for? (I read a lot of books and it is the same. It never says what the devil needs to be flexible for?) In order to be more powerful (the logic does not match, the devil is already very powerful. If it is said that it is powerful because of the human soul, then how does he lend his power to people, it is a bit confusing). If demons are divided into levels, how do lower demons become big demons? If human souls (unlikely) are so stupid, what is the use of the soul?

If you dare to come up with a four-character book title, I'll give you a thumbs up for it.

Brother, please delete the beginning of the first chapter. The protagonist's style of doing things is completely unlike a time traveler or an adult. It would be great if you directly wrote about the indigenous peoples of the world. Now readers can't stand the thought of a time traveler being so stupid. How nice that you deleted the time travel at the beginning.