Another scenario might be that Connor Kenway succumbs to an illness or injury that he has been secretly carrying. He tries to keep it hidden as he continues his duties as an assassin, but in the end, it becomes too much and he passes away, leaving a legacy behind in the Assassin's Creed Brotherhood.
A new villain could be introduced in the fanfic who is specifically out to get Connor Kenway. This villain might have a personal grudge against Connor or be on a mission to eliminate all the Assassins, and Connor becomes their prime target and ultimately falls to their schemes.
One possible scenario could be that he meets his end in a grand sea battle. Maybe his ship is outnumbered by a powerful enemy fleet. His crew, though brave, is gradually overpowered. Edward, fighting valiantly to the last, is finally struck down by a cannonball or a well - aimed sword thrust as he tries to defend his ship and his crew.
In a fanfic, they could be part of a grand adventure across the colonies. They get caught up in a mystery that involves ancient artifacts. Connor's knowledge of the land and his tracking skills, along with Aveline's ability to blend in and gather information in urban areas, would make for an exciting story as they race against time to uncover the secrets of the artifacts and keep them out of the wrong hands.
One possible scenario could be in the heat of a battle. Byakuya, facing an overwhelmingly powerful enemy, decides to sacrifice himself to protect his comrades. He uses his last ounce of strength to perform a powerful attack, but in the end, succumbs to his wounds and dies heroically.
One possible scenario could be Anakin sacrificing himself to save someone he loves, like his children or his friends. In this case, he might face a powerful enemy alone and use his remaining strength to defeat the foe but at the cost of his own life.
In a 'ahsoka death fanfic', one possible scenario could be her sacrificing herself in a battle against a powerful enemy. Maybe she faces an overwhelming force that she decides to take on alone to protect others.
Begin by creating a conflict that involves both Edward and Connor. It could be a new Templar threat that has roots in Edward's time and resurfaces in Connor's. Develop their characters further by giving them internal struggles. Maybe Edward is haunted by his past actions as a pirate, and Connor is struggling with his identity as an Assassin in a changing world. As you write, keep the pacing right. Alternate between action - packed scenes and more reflective moments. And most importantly, let your love for the Assassin's Creed series shine through in your writing.
A great plot twist could be that Aveline is initially working for the Templars, but she's actually a double agent. Connor discovers this halfway through the story and has to decide whether to trust her or not. It would add a whole new layer of tension and mystery to the fanfic.
A fanfiction could be about family ties. Maybe Connor discovers he has a distant relative who was part of Edward's crew. He sets out to find this person and in the process, uncovers more about his family's past. Along the way, he meets Edward's ghost or some kind of spiritual manifestation of him. Together, they work to protect a hidden Assassin stronghold from the encroaching Templars.
In a fanfic, he could die from a poison or a slow - acting toxin. Maybe he was on a secret mission and got poisoned without realizing it at first. As the toxin spreads, he tries to fight it but eventually succumbs. This could add a lot of drama as his friends try to find a cure but are too late.