Seban left Daffodil village when his betrothed, Sana was several months pregnant. In a seemingly sudden fall from grace to all outsiders, Seban fell to the ways of the scoundrel, and shirked his fatherly responsibilities, not intending to care for the young child Mitsuki, or to support Sana. Things turned for the worst however when he and a band of thugs he'd taken to, were arrested by Capt. Suika Meron (watermelon-melon) and sent to labor camps in the Grand Line.

Here, Seban received an opportunity for early release, and seeing his skill in Navigation, he was promoted into the Naval force to work off his sentencing under parole...

While in the Navy, (just three years after his initial capture,) Seban had officially earned his freedom from indentured service to the Navy. He returned from the Grand Line a 'reformed man', joining up as one of Captain Meron's chief Spies in the south blue, (the group's operations had, at this time moved closer to Mitsuki's home in Daffodil Village). He seemed to have the inside track concerning the plans of those who worked on the wrong side of the law, and his efforts were successful in bagging many a notorious outlaw and pirate. But, as often happens, Sebastian made a number of enemies in the process. One such group was a band of outlaws led by Eufaw the Giant. These came together to form the Eufaw Outlaws, and their sole purpose was to tear down the Naval presence in the South seas, particularly with regard to Meron's crew.

To attract the Navy's attention, the outlaw gang did the unthinkable... They ransacked the entirety of Daffodil Village, raiding, pillaging, and killing at will all who opposed them, and on top of this, they captured several dozen of the village's children, hoping to sell them on the black market to slavers.

Seban was in the middle of a military briefing when he heard the news, and in an outrage, he tore from rank, and began a desperate solo voyage back to Daffodil to see what could be done. All the way, the memory of his abandonment clawed at his heart. He arrived at his home to find it scraped empty as so many others were, and his heart sank, as he discovered that Mitsuki was indeed one of the children stolen.

Despair swept him then, and he would have given up hope for living if it weren't for Sana. She lay bleeding at the base of the town mill, on the brink of death. With her dying breaths, she told Seban to the best of her reckoning, where the outlaws were said to have been in hiding. She forgave him for fleeing their family and placed the well being of their three year old daughter, in his hands. She also gave him a map which told the secrets pertaining to the location her family's treasure horde.

Following the map's instructions to the burial plot, Seban began to dig. Seven feet down, he found a chest, filled with gold and other items besides - a devil-fruit of unknown properties, and two twin fine-grade daggers (belonging to Sana's father, Soba, a Navy man in his own right, long deceased). Seban took the daggers, and wolfed down the fruit, but left the treasure in the plot, as there was no safer place for it to remain at the moment... For two hours Seban retched and spat upon the ground. And then, drawing himself up, he returned to the village and buried his wife.

What would occur next is likely the most daring rescue attempt in all of ONE PIECE history ( not counting Luffy's escapades). Seban met with his Navy companion, Norse, a thick-limbed, red-headed Northerner who had followed Seban from HQ, and together, they charted a course for the hidden isle of captives. There, they slaughtered nearly the entire group of marauders, though Eufaw was able to escape in the end. Norse recounts the mad tale best, relating time after time when Seban would take on a deathly look and fly at his enemies in blinding speed, carving men at will with the ghastly power emanating from two curved daggers clutched in his hands...

Seban and Norse rescued the children in short order, and were declared heroes by the Navy and Daffodilians alike.

At the adventure's close, Saban and Norse decided to part ways - Norse returning to his detachment, and Seban to Daffodil. He remained with his daughter Mitsuki for several years, attempting to make up for lost time. He got a job in town and went about the arduous task of rebuilding their home. He had seemed, to so many villagers - once again, completely reformed.

Then one day, he received a letter from Cipher Pol 4. It was a limited time offer to train with them under Commandant Blacks and, to embark on a secret mission against Eufaw the Giant and his affiliated fleet. Seban's veins coursed with vigor, for he was a man of the seas now, and could not deny the challenge nor call for completing his revenge. Mitsuki, now six years old, knew he would leave upon reading it. He was a hard man, that her mother could not understand, and for her own part, she only wanted to see her daddy happy. One day, after returning from playing in a nearby field, she noticed the twin daggers missing from their dais on the wall. Also, pinned to the commons table was a note, written in the simple and gruff script Seban used:

"I'm leaving for a time. Take the Chest at the doorway and treat with your Aunt Doris to give you lodging.
I love you, Mitsuki."

At the doorway, the foot-and-a-half-high chest stood open. It's lock breached, Mitsuki saw that it was filled to the brim with doubloons and bill folds. Save the daggers and fruit, not a single piece of her mother's treasure was missing.

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Irezumi D. Nezha and Juan Sebastian Monticello have a long history that goes back to their time in the Navy. They met in the North Blue at a huge party hosted for a World Noble who was coming to tour the world. They had many drinks and talked at length about their desire for justice, to be able to make the world a better and safer place. Nezha's father's fleet, in which he and his brother's were captains, would be escorting the World Noble about in his Tour and Juan was shortly to join CP4. It would be several years before they saw each other again.

As a test of Seban's loyalty CP4 was assigned to wipe out a village, not unlike Daffodil Village, in order to provoke the pirate crew whose captain had originated there to return for revenge much like Seban himself. Nezha had caught wind of such a plot before departing from the care of those who had saved him and set himself against CP4 as the village's lone defender.

Upon seeing the members of CP4, Nezha and Juan immediately recognized each other. Nezha implored Juan to remember why he had been proud of his Navy service, that he would be able to seek justice for people just like the ones he had been ordered to destroy. While fighting and taking a tremendous beating from CP4, Nezha continued to plead with Juan to join him in making the world a better place, that if he did this he would be no better than Eufaw the Giant.

Juan realized that Nezha was right and turned on CP4. Their combined efforts were enough to drive back CP4, who retreated to HQ to report the betrayal of Juan Sebastian Monticello along with the survival and Devil fruit empowerment of Irezumi D. Nezha.