Heir Of Mythical Heroes is a Manga/Manhwa/Manhua in (English/Raw) language, Action series, english chapters have been translated and you can read them here.
Han Jungmin, who is only ‘top on in written exams’, gave up becoming an adventurer as he didn’t have the talent. After taking some time off from the adventurer academy, and as he started to write a fantasy novel… [You have been plagiarised by the world.] [Unique class – author of the story starts.] one day, the novel Jungmin wrote starts to become a reality and gets the job of being the ‘author of the story’. On top of that… [The only unique ability opens.] a special skill that nobody else has. Can Jungmin achieve his dream of becoming a dungeon adventurer?