Obviously, Harry and Tony Merchant are the main characters. Harry could be a heroic type, with special abilities or skills. Tony Merchant might be a more complex character, perhaps a bit of a rogue but with a good heart.
Perhaps it's a story set in a post - apocalyptic world. Harry and Tony Merchant were trying to survive. They got into a conflict with a brutal gang. During the fight, Merchant got fatally injured. Harry then had to carry on with Merchant's unfinished business and seek revenge.
The main antagonist could be Master. Since the title mentions Master, it's likely that this character has a lot of power and influence in the merchant world. They might be using their position to cause harm or manipulate things in a way that leads to death, which would make them a natural antagonist for Harry and Tony to oppose.
One possible plot could be that Harry and Tony are both merchants in a dangerous world. Master is a powerful figure who controls the market. Death starts to target the merchants due to some ancient curse. Harry and Tony must team up, using their skills as merchants to find a way to break the curse and avoid death, while also dealing with Master's underhanded attempts to take over their businesses.
The 'Merchant of Death' concept probably means that Tony is involved in activities related to death in a commercial way. For example, he might be selling things that can cause death, such as weapons or poisons.
I'm not sure who Tony specifically is in this fanfiction without reading it. It could be an original character created by the author, or perhaps a reimagined version of a known character in a particular fictional universe.
Another theme is self - discovery. Tony realizes that his identity as a weapons - maker isn't all he wants to be. He starts to explore other aspects of himself, like his ability to be a true hero and protector. In some fanfictions, he discovers new values and beliefs that change his perspective on life. For example, he might start to value human life more than profits from weapons sales. This self - discovery often goes hand in hand with his journey of redemption.
There could be an antagonist in the fanfic. Maybe someone who had a vendetta against Harry Merchant and was somehow involved in his death. This character would add conflict to the story as the people left behind try to figure out what really happened to Harry.
One possible storyline could be that Harry Merchant was a heroic figure, and his death led to a series of events where his friends or family members discovered some hidden secrets he had. They then used these secrets to right wrongs in the world he left behind.
One possible story could be about Tony's moral struggle within the 'Merchant of Death' scenario. Maybe he tries to find a way to redeem himself from his dark deeds. For example, he might start using his skills to protect the innocent instead of causing harm.