One interesting concept could be a crossover with a fantasy world like Middle - earth. Imagine an assassin having to navigate the perils of Mordor while still maintaining their creed. Another concept might be a crossover with a historical event not directly related to the main Assassin's Creed timeline, such as the sinking of the Titanic, where assassins could be on board for a secret mission.
In my opinion, 'Assassin's Creed II' has an excellent story. It follows Ezio Auditore da Firenze on his journey of revenge and discovery. You get to see his growth from a young nobleman to a master assassin. The historical backdrop of Renaissance Italy adds so much depth and richness to the narrative, with all the political intrigue, family drama, and the exploration of the Assassin - Templar conflict.
I think Assassin's Creed: Origins has an excellent story. It takes us back to ancient Egypt, a setting full of wonder. You play as Bayek, a Medjay. The story delves deep into the origins of the Assassin Brotherhood. It's not just about the assassinations but also about Bayek's personal journey to avenge his son. The historical accuracy and the way the story unfolds, with political intrigue and ancient mysteries, make it a top - notch story in the series.
Writing a good Assassins Creed crossover fanfic is all about balance. You have to balance the elements of Assassin's Creed, like the hidden blade and the assassin's parkour skills, with the elements of the crossover. Let's say it's a crossover with a detective story. You can't overshadow the detective's investigation skills with the assassin's combat abilities. Also, create believable relationships between the characters. If an assassin teams up with a detective, there should be some initial mistrust that gradually turns into respect and cooperation as they work towards a common goal.
For a beginner, Assassin's Creed II is a great choice. It has a relatively straightforward story to follow. Ezio's story of revenge is easy to understand and gets you hooked quickly. The game also does a good job of introducing the Assassin's Creed lore in a way that's not too overwhelming. You get to experience the beauty of Renaissance Italy while following Ezio's journey to become an assassin and take on the Templars.
Another great fictional assassin is Beatrix Kiddo, also known as The Bride from 'Kill Bill'. She has been trained in various martial arts and sword fighting techniques. Her quest for revenge showcases her tenacity and ability to take on numerous foes. Despite facing many challenges, she uses her skills to cut through her enemies on her path to vengeance.