A useless programmer from the 21st century travels into the popular Japanese manga "Demon Slayer: Kimetsu no Yaiba" and survives to the end by relying on the evil system and the entire plot to defeat the BOSS with the protagonist group (most of them survive)
The writing is not very good, so just read it as a cool article.
Intention: Time travel into Demon Slayer: Kimetsu no Yaiba