I was browsing through manga on my phone and found a manga version of this. I did some research and it turns out it's a novel.
Anybody interested in making a pdf version
btw https://www.novelupdates.com/series/demon-king-retry/
I've created an EPUB of the available chapters.
http://www.vn-meido.com/k1/index.php?topic=6551.0