Issac D. Tremau/History

Past
Around 11 years ago, Issac started living on his own in the streets.

A New Dawn Arc
Issac was hiding from the Marines on top of a building, when a Devil Fruit was suddenly flung toward him. Despite not knowing what it was, Issac ate it because he was hungry. He was then thrown another Devil Fruit with a bite in it by Drew Grenza, causing the Marines to notice and chase him.

Issac easily outpaced his pursuers, catching up to Drew, who was also being pursued. Drew begged Issac to help her, but he refused. Issac attempted to climb a building and slipped, but he grabbed a pole with his foot using his new Saru Saru no Mi powers. Drew managed to elude her pursuers by creating a cart from a drawing, and told a beleaguered Issac to join her. The two barreled through the streets, accidentally running into a boy named Hugeo. Hugeo revealed he also had fruit powers, and the three managed to escape.

In a hidden area, the three introduced themselves to each other, and Issac developed a dislike of Hugeo. Hugeo offered the chance to ask his Marine dad for help, and Issac reluctantly accepted due to there not being a better option. However, Issac's hatred of Marines caused him to antagonize Hugeo, resulting in Hugeo having a fit that attracted the Marines. Shoving Hugeo out of the way to keep him from being criminalized, Issac and Drew attempted fighting the Marines, but were easily defeated and captured.

Issac and Drew were taken to the Marine base prison, where they met Commander Drimble. Drimble threatened to drown them to get them to reveal Hugeo's location, although he would later kill them anyways. The two met Kal Rydan in the adjacent cell, who revealed that he stole the Devil Fruits they ate.

Fed up, Drimble finally decided to kill Issac and Drew by drowning them. Before they became submerged, however, Hugeo came and rescued them, along with Kal Rydan. The four of them then escaped through an air duct. However, the Marines were ordered to unscrew all the air ducts in response to this, and the four were eventually discovered. Issac, Drew, and Hugeo ran away while Kal confronted the Marines. They eventually reached the roof, where they were confronted by Drimble.

Drimble revealed that he had found out Issac has the "D" in his name despite all the D's supposedly being exterminated. He then took on the trio in battle. Issac, using newfound control of his Devil Fruit to undergo partial monkey transformations, fought Drimble alongside Drew and Hugeo, and the two managed to bring him down.

With Kal rejoining them, Issac, Drew, and Hugeo quickly escaped the Marine base. They intended to go to the harbor across Merceaux so they could leave, but were pursued across streets and rooftops by Marines carrying explosive launchers. Eventually, they managed to escape the Marines and head for the harbor. They met Silas, Hugeo's dad, who accepted defeat but warned the three that they were taking a very dangerous path. With no real place to go, the three agreed to go with Kal to rejoin his captain, Kraft.