This is a pretty neat idea! Let's have a shot at this, why not?
(I guess this doesn't count as a whole fic, but an extension of a headcanon? But whatever!)
It started as a normal day off for Kim Rok Soo. He went to the library, checked out the whole fantasy series called "The Birth of a Hero", spent the afternoon reading up to the fifth volume, and fell asleep.
When he woke up, he was hatching from an egg. Yes, you heard that right.
For some reason, he reincarnated into a Dragon. In the world of the very book series he was reading. An infant Crimson Dragon.
When he opens his eyes in this new life, he is alone.
Which is perfectly fine by him. Dragons are solitary beings, anyway. And he isn't a normal baby Dragon anyway; he still possesses the mind of a 36-year-old human adult, with all his Records intact.
Near the nest he hatched in, he finds a diary. Apparently his mother hid him from some crazy humans trying to hunt Dragons. In the diary, she promises to return after she deals with them. Kim Rok Soo has a sinking feeling she is never coming back.
Unfortunately, he is right.
But Kim Rok Soo decides that this new life isn't all that bad. He's a Dragon now, basically one of the strongest beings in existence. There are no expectations on him to intervene with the plot of the story: Choi Han never met any Dragons aside from that crazy Black one raised by Venion Stan.
Kim Rok Soo quickly figures out how magic works, and polymorphs into a human resembling his old self, except now his hair is red, and his face much prettier. Then he heads to the nearest human settlement - turns out his nest was located in a forest in the Breck Kingdom - and finds out the current date.
...He is two years before the start of the plot. One year before Choi Han finds Harris Village.
Kim Rok Soo decides - for totally logical, selfish, absolutely-not-altruistic reasons - that he should probably do something about it. "It" being Choi Han lost in the Forest of Darkness, and the two-year-old Black Dragon being tortured by Venion Stan.
It's the easiest thing to find Choi Han and convince him that them meeting is a simple coincidence. He as a young Dragon, you see, he doesn't owe anyone explanation why he does things; and anyway, making his lair in the Forest of Darkness seems perfect. Being one of the Forbidden Regions, it will certainly make the perfect place to stay hidden when the war it breaks out around the Western Continent.
In a moment of distraction, he introduces himself as Bob. Kim Rok Soo dearly regrets this thoughtless choice later on, but he's too lazy to change it. He will forever be known as Bob the Crimson Dragon.
Choi Han is, naturally, extremely grateful to his Dragon savior. It takes no effort at all to convince him to help rescue another Dragon from slavery. Bob the Dragon wants to keep low profile, after all.
So Choi Han and Bob rescue the two-year-old Dragon, and Bob names him Raon Miru. ...Only then Bob realizes his error, as these two seem absolutely attached to him now. What will happen to the plot of the Birth of a Hero now???
...Well, no crying over the spilled milk, Bob decides. If Choi Han doesn't decide to go on the journey by himself, he might as well guide him there. The help of a super powerful being as a Dragon - two actually, since Raon joins in as well - might help the plot go a lot faster and smoother.
Surely, nothing will go wrong with this plan!
...Two years later, Bob the Dragon is utterly confused.
There are people inside his Forest of Darkness Villa. All the time. As if his house was the hottest tourist spot around the continent.
Somehow - and Bob swears, he has no idea how - on top of the Protagonist and the Black Dragon child, he got saddled with an Ancient Golden Dragon, a ghost White Dragon, a Beige Farmer Dragon, a Pink Tween Dragon, 2 Cat Beast children, a whole village of Wolves, several Whales, an Elf healer, secret-Dark-Elf prince, a wish-to-be-ex-princess mage, an ex priestess, and many others.
Bob the Crimson Dragon looks at the chaotic zoo that is his house, filled with people looking at him with uncomprehensive admiration, and despairs.
It wasn't supposed to be like this...!