Haven Kenway's novel could potentially explore various elements such as character development, complex relationships, and unexpected plot twists. But without more information, we can only guess at the specifics of the story.
There's a good chance Haven Kenway is the lead. However, sometimes in novels like these, the definition of a protagonist can be fluid and might change as the story progresses.
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.
One possible plot could be that Connor, being from a later time in the Assassin's Creed timeline, stumbles upon some ancient records or a hidden memory that leads him to Edward. They might initially be at odds due to their different time periods' ways of life. Edward, being more of a swashbuckling pirate - assassin, could teach Connor some new combat techniques or ways of navigating the high seas that Connor hadn't experienced in his mainly land - based adventures. They could also bond over their shared goal of fighting the Templars, with Edward sharing his experiences from the earlier days of the conflict and Connor bringing in his knowledge of the more evolved Templar plans in his time.
A common theme is legacy. Since she is Edward Kenway's daughter, many fanfictions explore how she either lives up to or rebels against her father's piratical legacy. For example, she might try to complete some of his unfinished business or go in a completely different direction to distance herself from his name.
In the Kenway family story, the first major event was Edward Kenway's life as a pirate. He sailed the seas, fought battles, and got involved in the Assassin - Templar affairs. His son Haytham's transformation into a Templar was a crucial turn. Haytham was trained in the ways of the Templars and had his own set of goals. When Connor, Haytham's son, decided to be an Assassin, it set off a chain of events. There were family meetings filled with tension, battles between the two factions involving the family members, and a continuous struggle between the family's different ideologies.
There's a fanfic where Edward Kenway's daughter is on a quest to uncover some long - lost treasure that her father had once sought. It delves into her character, showing her determination and the skills she learned from her father, like swordsmanship and navigation. The story is full of action and adventure on the high seas.
Another possibility is a former crewmate turned traitor. This crewmate could have been jealous of Edward's leadership and the share of the loot he got. So, the traitor could plot with other pirates or even the enemy. They could stage a mutiny at a crucial moment, like when they are about to face a big battle or are in the middle of a difficult sea journey. During the mutiny, the former crewmate could be the one to deliver the fatal blow to Edward.
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.
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.
I'm not sure specifically as there could be many different 'haven game stories'. It might be about the adventures in a haven, like the characters' experiences in a safe or special place within the game.