Isaac is the main antagonist of the game One Piece: World Seeker. He is the prison warden on the World Government-affiliated Jail Island and a scientist who serves as the island's highest ranking Marine officer. He is also Jeanne's older brother.
Isaac is a tall man with wild blue and brown hair that is slicked back except for a blue lock of hair that hangs loose on the left side. He has a dark and wide scar that goes across his right eye from his forehead and has cleft chin with slight brown beard. He wears a pair of glasses and a black buttoned suit with a green collared shirt and an orange tie under a white lab coat and a high-collared coat that is blue on the outside, but has brown fur on the inside. He pairs this with blue suit pants, black shoes, and black gloves that he wears over his robotic hands.
When he was young, all his hair was blue and he did not have a beard.
Isaac is a vindictive and serious man who sought revenge against the World Government for their attempts in trying to claim his home island to harvest Dyna Stones. These attempts include the death of his and his sister Jeanne's own mother which acts as the catalyst of his vendetta. This hatred also stretched out to pirates and others alike as he saw them as bad, if not worse, as the World Government.
His desire for revenge deteriorated his overall moral as he was even willing to sacrifice the islanders to ensure he had his revenge. This lack of empathy made him go as far using his own sister, Jeanne.
According to Jeanne, Isaac use to be a kind person who loved the island and wanted to protect both it and its people.
As a scientist and a high ranking Marine Officer, Isaac is extremely intelligent as he is able to implement elaborate plans and utilize advanced technology.
During his final confrontation against Luffy and Jeanne, Luffy points out how weak and cowardly he is compared to Jeanne because of how he left the island and put on armor to isolate himself from both Jeanne and his home. After being defeated, he slowly began showing remnants of his former kind self after hearing how much Jeanne was putting the island before herself, which included her own resentment towards the World Government, for the sake of their mother. He then becomes selfless by saving both Luffy, although claiming how he still hated the pirate, and Jeanne from the Sky Prison before it self-destructed from the Dyna Stones while also ensuring that the World Government would be unable to harvest any of them.
Isaac loved his mother dearly and originally shared her dream in protecting what was, at the time, named Jewel Island, and is now Jail Island, and its islanders. Her death changed him drastically into a vindictive man who secretly sought revenge against the World Government for playing a role in his mother's death.
Jeanne is Isaac's younger sister. In the past, they used to be very close, sharing their mother's dream to protect their home island. However, they ended up on bad terms when Jeanne began opposing her brother and the Marines' tyrannical rule over Jail Island.
Straw Hat PiratesEdit
Abilities and PowersEdit
Isaac has significant authority and power, as Smoker is shown to be subordinate to him while he is on Jail Island. Smoker refers to Isaac as his superior, and even ending his fight with Luffy because he is called back by Isaac. Likewise, even Borsalino, a Marine Admiral, stopped fighting Luffy when he was told to by Isaac. 
Isaac is a cyborg with cybernetic enhancements on his arms and legs. Thanks to these, he possesses tremendous physical strength and speed, being able to overpower Luffy with his blows. He is capable of blasting his hands away, allowing him to attack people from a distance with them. He can also electrify his cybernetic attachments, similar to Electro. His cyborg arms are made of Seastone which grants him a huge advantage over Devil Fruit users.
Isaac was born the son of Jewel Island's former leader. After his mother passed away, he decided to join the Marines, where he rose through the ranks. Eventually, he was promoted to the position of warden by the World Government for the purpose of researching and excavating the Dyna Stones on Jewel Island, and returned to the island to take command.
One Piece: World SeekerEdit
When Monkey D. Luffy is captured, he is brought to Isaac who welcomes him to Jail Island. However, when the Straw Hats realized that the island had no treasure and that it was a trap, Luffy broke out of the handcuffs with Robin's help. Isaac then approached Luffy and choked him with his detachable robotic hand, causing the two to engage in a battle. He easily overwhelms Luffy with his Seastone hands, but Luffy escapes when Isaac is distracted by a Marine reporting to him. Luffy then jumped off the Sky Prison back down to the island below.
Afterwards, Isaac and his entourage passed through Steel City, where Luffy saw him and was about to attack, but was held back by a pro-Marine civilian.
Sometime later, Isaac and Roronoa Zoro engaged in a battle, where Isaac praised Zoro for being stronger than he had thought and commented that it was worthwhile for him to collect data on the pirate himself. Isaac then pointed out to Zoro that Luffy had arrived and prepared to leave due to other business. He then ordered his robots to attack the two pirates and then left during the battle.
Later, during Luffy's battle with the Marine robots in Sapphire Town, one of the robots leapt out and attempted to attack Jeanne, but before it could do so, Isaac jumped in and took it out. Upon seeing Isaac, Jeanne reveals that he is her brother and asks him where the robots came from. He then replied that the robots belonged to the Marines but had been stolen from storage. Afterwards, he states that he must take his leave, but Jeanne continued to question if the robots were truly stolen, to which Isaac replied if it seems like he would lie. Jeanne then responded that she was unsure of whether he would lie, but that she knew he had changed. Hearing this, Isaac emphasized that he was not the one that changed, but instead, it was the island that had. Jeanne, instead, insisted that the reason the island felt like it had changed was due to the presence of the Marines, but Isaac rebuked this claim and stated that the islanders themselves wanted change and that the island's state of affairs was a result of that and not because of the Marines. Before they could continue, Luffy interrupted them and questioned why a brother would not help his sister, to which Isaac stated that he had already told her to leave the island and that it was pointless to continue to discuss it if she wouldn't listen. He then thanked Luffy for protecting Jeanne and the islanders and commented that even pirates have good ones before leaving and saying that Luffy was helpful in helping him collect data and that the pirate would be of use.
Back in his office, Isaac received a call that reported that the Germa 66 had arrived. He told the other person on the line relay to them the time and place of transaction and warned him to be careful, as to not let the Marines find out about it. When he asked about the other pirates, the mysterious caller stated that they were continuously making their way to the island, but then informed him that their intel showed that CP-0 was dispatched to the island as well. In response, Isaac calmly replied that he already knew CP-O's motives and that they weren't to be worried about for now.
Later, as Rob Lucci ran from Luffy, Isaac surprised and attacked him. The injured Lucci then questioned Isaac about what he did with the money from the black market and whether or not he had ever planned to honor his part of the agreement with the World Government on excavating the Dyna Stones. Isaac refuted this claim and stated that the data that he had been reporting to the World Government had been real and that he was doing his part. However, he reveals that he had intentionally failed to report that he had already finished excavating the stones. He then prepared to kill Lucci, but was interrupted by Luffy, allowing Lucci to escape. After Jeanne arrives, she questions what his intentions with the Dyna Stones are, and asked him how he could go against their mother's will of preventing their excavation. However, Isaac argued that their mother would have died in vain if he did not do what he was doing now, which is to destroy everyone who seeks the stones. After some more discussion, Isaac took his leave.
Afterwards, when Jeanne gathers the islanders in the plaza, Isaac confronted her and revealed his true intentions, which were to take revenge against the World Government for killing their mother. He then told Jeanne that it was the World Government that had hired the pirates to attack the island and that he had been planning all this time to instigate a war between the Marines, pirates, and islanders, all of which must die. Hearing this, Jeanne attempted to run back to the plaza to warn the islanders, but before she could reach them, one of Isaac's inventions attached itself to her and, using her as a vessel, turned into a robot. Before leaving, Isaac said that if anyone were to be blamed, it would be herself for changing and Luffy for changing her.
Back at the Marine Base, Luffy confronted him and questioned him why he would do that to Jeanne. Isaac explained that with her out of the way, the island would fall into chaos and that she would have no choice but to leave the island. He then mentioned that it was to late to stop again and left abruptly.
Eventually, Luffy and Jeanne make it onto the Sky Prison. Jeanne approached Isaac and continued to question how exactly he planned to get revenge with the Dyna Stones. In response, Isaac reveals that he will use the Dyna Stones to destroy Mary Geoise by crashing the entire Dyna Stone-loaded Sky Prison into its center. Jeanne tried to convince her brother not to do so and mentioned how their mother had died to prevent the stones from becoming a weapon, but Isaac simply pointed out that she accomplished nothing by dying for the stones. Instead, Isaac emphasized that he would prevent anyone from getting the stones by destroying all those that seek it along with the stones and only then would their mother's dying wish be fulfilled. However, Jeanne strongly disagreed and vowed to stop him, but before she could do anything, Isaac approached her and knocked her out. Seeing this, Luffy jumped into action and sprang at Isaac, but Isaac dodged and then equipped his robotic suit. The two then engaged in battle, but after some time, the two paused as Isaac had become exhausted. During this pause, Isaac demanded to know why he would help Jeanne, to which Luffy replies that Jeanne wanted to save him. Isaac laughs this off, but when Luffy comments that he is weak because he cannot face Jeanne without taking off his armor, Isaac becomes enraged and powered up his suit even more.
Throughout their battle, Isaac continued to ask how he could be weak if he was willing to give everything up, and although he eventually pinned down Luffy and sent an explosion out from his suit onto the pirate, Luffy destroyed part of the armor. An enraged Isaac then questioned what he had done wrong and charged at Luffy, attacking him while asking why the pirate, Jeanne, and his mother were strong, and how he had failed to achieve that. Luffy, however, did not care and sent a punch straight into Isaac's face, destroying the helmet. Isaac then fell to his knees and, before fainting, commented on, if anything, he knew for sure that he despised the pirate.
While unconscious, Isaac had a dream about his mother telling him to protect the island. Before long, he is woken by Jeanne calling to him. With him awake, Jeanne kept telling him to do something about the Dyna Stones, as the prison was slowly descending onto Jail Island. Isaac then asked her if she had thought about getting revenge for their mother, to which she responded she had, but that she cared more about protecting the island. Upon hearing this, Isaac broke into happy laughter. He then got up and told Jeanne and Luffy that he would blow up the Sky Prison along with the Dyna Stones to prevent the World Government from getting them, and that he would try to get as far away from the island as possible. Afterwards, he walked over to Luffy and lifted him to the edge of the prison, tossing him over so that he would not be caught in the explosion. When Jeanne ran towards the edge, Isaac detached his armor and attached it to her so that he could send her off. However, she begged him not to abandon her, but he simply told her to protect the island for their mother. With that, the Sky Prison fell into the sea and exploded with Isaac still on it.
Some time later, after the Straw Hat Pirates and Trafalgar Law left, Jeanne visited their mother's grave and discovered that Isaac had survived the explosion when she sees him there.
- The short biography of Isaac that was released before the game stated that he is a former Marine. However, within the game itself, Rose, a Pro-Marine civilian in the game mentions that Isaac is the highest ranking Marine officer on Jail Island.
- ↑ 1.0 1.1 1.2 1.3 1.4 , Weekly Shonen Jump 2018 Issue 42; Isaac is revealed.
- ↑ 2.0 2.1 2.2 , One Piece: World Seeker Wesbite — https://opws.bn-ent.net/sp/news/13.html
- ↑ 3.0 3.1 3.2 3.3 3.4 , One Piece Video Games — One Piece: World Seeker, Isaac debuts.