Six years had passed since the departure of Sakazuki, Momonga, and Onigumo.
The year was now 1517.
In the waters of North Blue, a Marine warship was sailing steadily across the sea. Marines were busy on the deck, managing the sails and the helm. At the very front of the ship stood a young man.
That man was Kai.
He was now seventeen years old.
Over the years, he had grown taller and more mature, his presence calm yet heavy. Draped over his shoulders was the coat of a Senior Lieutenant, the symbol of his rank fluttering behind him in the sea wind.
Seven years… Kai thought quietly.
Seven years since I was reborn into the world of One Piece… and became a Marine.
After Sakazuki, Momonga, and Onigumo had left, Kai began training under Yamakaji, just as Sakazuki had promised. Yamakaji proved to be an excellent instructor—calm, patient, and always precise. He corrected Kai's mistakes without anger and often spoke about many different things, not only battle.
Under Yamakaji, Kai learned close combat and swordsmanship properly.
Later, Yamakaji began teaching him the Six Styles of the Marines:
Geppo, Soru, Shigan, Kami-e, Tekkai, and Rankyaku.
At first, it was extremely difficult. His body failed him again and again. Only through relentless effort did Kai manage to learn all six styles. Among them, his favorites became Geppo, Soru, and Shigan.
He could use all six—but only those three could be naturally combined with his Mist Devil Fruit.
As Yamakaji once said, if Kai learned to merge the Six Styles with his Devil Fruit, his fighting style would become unique.
And so he did.
Later, Yamakaji even began teaching him the final two advanced techniques: Life Return and Rokugan. These were far more difficult. Kai struggled greatly, and it took him two full years before he could use them properly.
After mastering the Six Styles, Yamakaji granted Kai the rank of Junior Lieutenant, and soon after entrusted him with his own Marine unit and ship. From that moment on, Kai began hunting pirates and mafia organizations across North Blue.
That was when the nightmare began.
Thanks to his mist, Kai could always find his enemies. Pirates and mafia groups could not hide—on land or sea. Even taking hostages did not save them. His mist warned him in advance.
Thus, his nickname was born:
"The Bloody Mist."
Kai never stopped until all his enemies were dead. His mist was often stained red with blood. To pirates and criminals, he was a monster.
But to civilians and Marines, he was a hero.
His greatest achievement came later.
Kai finally learned how to cut metal with his sword—and how to release flying slashes.
This happened during the most dangerous battle of his life.
Surviving mafia members, pirates, and even several Devil Fruit users united to kill him. They prepared an ambush at sea, having learned that Kai's mist was less effective on open water than on land.
Dozens of enemy ships surrounded Kai's vessel, firing nonstop cannon volleys.
For the first time, Kai felt true pressure.
The situation was so dire that Yamakaji himself arrived, along with several Marine ships from other bases. The battle lasted an entire day and became the bloodiest conflict North Blue had ever seen.
The Marines won.
All pirates and mafia forces in North Blue were completely destroyed.
But the cost was devastating.
Fifty regular soldiers died.
Twenty non-commissioned officers.
Ten midshipmen.
Eight lieutenants.
And four captains.
Even Yamakaji and Kai suffered severe injuries.
The reason was simple — they were fighting against the strongest enemies, among whom were Devil Fruit users of the Zoan and Paramecia types.
Yamakaji endured it with experience, but for Kai, it was his first battle against multiple Devil Fruit users—Zoan and Paramecia alike. Worse still, several enemies used seastone, which became a serious weakness for him.
Yet within that desperate battlefield, surrounded by blood and death, Kai awakened something new.
Under extreme pressure, using the Hidden Mist Technique to protect his allies, he finally learned how to cut metal.
That battle shook the entire Marine force of North Blue.
Because of the losses, Yamakaji personally requested assistance from Fleet Admiral Sengoku.
After the war, Sakazuki contacted Kai, asking how he was and how he felt. Even after leaving and later becoming Akainu, Sakazuki continued to call him from time to time—asking about his training, or telling stories of pirates he had personally destroyed.
Now, officially, North Blue had become as calm as East Blue.
But Kai knew…
This peace would not last.