First, a disclaimer: the author is a no-nonsense straight guy, and so is the protagonist!
[Devil Fruit + Haki] [No System] [Almost Invincible]
He transmigrates as Portgas D. Ace, son of Pirate King Roger, and obtains the Flame-Flame Fruit.
He develops all kinds of flame-based techniques.
In Pirate King, Luffy is always portrayed as clueless and uneducated. But things change after the protagonist transmigrates. Luffy may not be eloquent, but the protagonist helps him develop a basic understanding of the world from a young age.
Do you have to be a pirate to overthrow the world? No, no, no!
This world will be toppled and rebuilt by the three of us brothers!
P.S. This isn't a mindless, hot-blooded story. The protagonist doesn't have chuunibyou or a chuunibyou spirit, either. As for the other elements mixed in with Pirate King, they were recommended to the protagonist by his daughter before he transmigrated. He knows a little about the plot, but not much (I'm the same, actually), so I'll change many details from the original according to my own understanding. If that bothers you, don't read.
[Flame Emperor: Fallen Heart Flame]: His body constantly produces inner fire, tempering his Armament Haki every moment. It's known as a one-click training cheat for Armament Haki!
P.S. There are a few elements from other works, but very few. You can easily enjoy this even if you haven't read those works. There are no items from other worlds; the only golden finger is transmigration.
Five Elders? Take this [Flame Emperor: Heaven and Earth as One]!
Also, what would happen if Luffy and Sabo were raised to be cultured from childhood?
With Luffy, Ace, Sabo, and a group of like-minded people blessed with great destiny, they will form a force powerful enough to overturn the entire world!
