Okay here is my SU, I hope this is okay.
Home: Loka in The Grand Line (Fictional) – Loka is a small, poor island with only a moderately sized village on it as settlement. Loka is a warm temperatured Spring island but does sometimes experience heavy rain, it is this balance that allows the unique plant-life to survive on the island. The island has been a target by both Marines and Pirates alike due to the wide range of medicinal plants found on the island.
Occupation: Doctor, especially knowledgeable on poisons and physiology
Setting: Bounty Hunter – Marcus has operated underground for some time now using his knowledge of toxins and the human body to take in, or take out targets... for the right price.
Appearance: Marcus has what appears to be an average, thin body but despite this appearance is physically fit and reasonably strong due to training of his body for his work as a bounty hunter. He has shaggy, long black hair that is short on the sides and a messy fringe and his eyes are deep and dark blue in colour. He usually have messy black stubble on his chin.
His typical attire consists of long, baggy black pants with torn bottoms on the legs, a simple white, short sleeved shirt and long, tawny brown coat that reaches to below his knees. He usually wears this coat open but in particularly cold weather it will be closed. His has a black, leather belt around his waist with several brown pouches that contain medical tools and poisons attached to it. He wears short, lace up brown boots and has a pierces left ear which has a small chain with a gold ball hanging from the end in it. He also has a thin scar just under his left eye that extends vertically down to about half-way down his nose. He is often described as having a gruff, yet neat appearance. He is generally considered to be not particularly attractive but far from ugly, he doesn't stand-out in a crowd witch is sometimes an advantage in his line of work.
Personality: Marcus tends to be a sarcastic person and has a jokey, adventurous and entertaining side to him, not to say that he can’t be serious when he needs to be though. He’s generally respectful to people and is loyal once befriended but has a particularly nasty and sadistic side which is usually aimed towards those he doesn't like. Those who know him tend to recommend you don’t do anything to earn his distrust, he has a distaste for those who are disloyal. He doesn't talk about his past much, because he feels his beliefs about loyalty are unjustified due to how he abandoned his home on the Grand Line. He has few things he particularly enjoys with the exceptions of gambling and a bizarre hobby for experimenting with medicine and poison. He becomes particularly annoyed by bad attempts at first aid, people who underestimate him and those who refuse to take action when it is necessary, even if it is to help themselves. He has a tendency to chide people for childish attitudes. He is also kind of touchy as to what the “L” in his name stands for.
Goal: It is hard to define his goal. He simply wants to make a living through his work and to explore the world. He doesn't particularly want to be rich, but won’t complain about making some decent money. He intends to find a former partner on a job and torture and kill him (see background). He also has an interest in seeing Loka again but is rather nervous about this due to the manor in which he left.
Weapons: Marcus uses a fairly wide range of weapons consisting of darts, scalpels and short, flat blades that are, more often than not, poisoned with some sort of toxin. He will also sometimes use vials of these toxins alone and when necessary knows the body well and is competent in hand-to hand combat. He is experimenting with toxins that could neutralise devil fruit but has been largely unsuccessful.
Powers: Marcus has extraordinary aim which when combined with his kills with poisons and knowledge of biology/physiology can make him a deadly opponent. When not using ranged methods of attack Marcus uses a fighting style revolving around hitting weak points on the body and pressure points or cutting vital point with a scalpel or blade. His main weaknesses are his inexperience with fire-arms (although he’d like to learn at some point) and that his opponents tend to be physically stronger than him or posses a devil fruit.
Background: Marcus was encouraged to be passive as a child and as such rarely got to act out his more adventurous wishes. He instead helped his father, the islands main doctor, gather useful medicinal plants. It was through this and his fathers teachings that he came to learn medical skills. At the age of about eleven he had taken a huge interest in medicines and although he wouldn't tell his father and mother, toxins. It was also around about this time that the surprisingly quiet (due to its location) little island began to see more traffic from pirates and due to this the navy. The pirates would often raid the village for its vast medical supplies or force doctors such as Marcus' father to aid their injured. The navy that moved to the island to keep an eye on pirate activity were a lowly ranked bunch of rowdy, corrupt drunkards who were almost a dangerous and bad for the local resources and people a the pirates. Marcus had a difficult time understanding why nobody stood up to either group, especially when skirmishes between the two began affecting the community of Loca, nevertheless he never got involved.
One day, when he was thirteen, during a particularly large battle between pirates and the navy Marcus ended up getting cut below his left eye, but he was lucky since several others died. That moment was when he decided that both groups had to go. He continued to refine his understandings of medicine and poisons, not just with the intention of healing, but with the intention of fighting back next time he was in danger. Eventually these studies led him to become one of the islands doctors at the young age of sixteen, needless to say he was very talented, especially with curing ailments caused by toxins. Despite his success Marcus was becoming more and more disillusioned with the islanders and their passive nature, being a doctor and helping aid the people he despised as well as their victims didn't help
At seventeen the biggest battle between the two groups yet occurred. He ran around, helping the injured during this time and saw many familiar faces die at the hands of pirate and marines, including his mother. A marine pulled out a pistol and shot her point blank in the face, it was clear she wasn't an enemy, he just did it, but what hurt him even more was that his father had been standing next to the pirate as he pulled the trigger and done nothing. Marcus later found out that his father had traded her life for his own. Enraged Marcus not only stopped hiding behind the peaceful, mask he had adopted but even in that moment through his kind and generous side away, he took a scalpel and poisoned it with sea-snake venom and took to pirate and marine alike throughout the rest of the battle. When it was over he buried his mother and several of his friends and set out to kill his father, not hard on a small island, but as his father cowered at his feet he decided that the man deserved to live with his sons hatred and the knowledge of his betrayal. Marcus left the island shortly after, selling his skills as a bounty hunter.
In his travels as a bounty hunter Marcus would sometimes become bogged down by his work, some of the people he had to hunt were people just like him, honest hard working people, but he had to do something to affect the world, he couldn't bare for people to no longer take action against their enemies, even if it meant being a weapon. He took to gambling and drinking to ease the burden he sometimes felt and to forget about Loka, but he couldn't help but want to return and see what had become of his home, though he didn't dare.
On his last job he had been chasing a vicious pirate and had been forced to team up with another bounty hunter. They worked well as a team and easily caught their target but his partner double crossed him. After a night of celebration the drunk Marcus' collaborator drugged him with one of his own poisons, beat him thoroughly and pushed him out to sea in a rickety boat with no oars. A few days later he woke up on the shore of Ruedaya, sore, disoriented, dehydrated unsure of where he was and strangely, able to remember almost everything except the identity of his assailant. He would very much like to return the favour if he could remember who his target was.
Let me know if anything needs changing. I have made made it a bit easier to read and a bit more specific.