A more adventurous plot could be Saber Lily and Shirou going on a quest. They are searching for a magical artifact that has the power to save Camelot from an impending doom. Along the way, they encounter various mythical creatures and face many challenges that test their bond and their individual abilities.
One interesting plot could be Saber Lily and Shirou teaming up in the Camelot era to face a powerful, previously unknown threat. Maybe a dark sorcerer who is trying to corrupt the very essence of Camelot. They would have to rely on each other's strengths, with Shirou's determination and Saber Lily's combat skills.
Another plot might involve a love story. In the Camelot setting, Saber Lily and Shirou could gradually fall in love as they fight side by side for the greater good of Camelot. Their relationship would be complicated by the rules and expectations of that time, but they find a way to be together in the end.
For Shirou, his character can be developed by showing his growth in combat skills specific to the Camelot era. He could learn new sword - fighting techniques from Saber Lily. His ideals can also evolve as he experiences the different values in Camelot, becoming more confident in his own beliefs.
One great shirou x saber lily fanfiction could be 'A New Beginning'. It explores their relationship in a post - Holy Grail War world where they have to rebuild and find their place together.
One idea could be Shirou trying to understand Saber Alter's dark past in Camelot. He might discover the events that led to her becoming Alter. Another could be them teaming up to face a new threat in Camelot that neither could handle alone. Maybe a powerful mage is trying to rewrite the history of Camelot and they have to stop it.
You can try Archive of Our Own (AO3). It has a large collection of fanfictions, and you are likely to find many shirou x saber lily ones there. Just use the search function.
It could start with distrust. Saber Alter is different from the original Saber, and Shirou might be cautious. But as they face challenges together in Camelot, like battles against dark creatures, they start to rely on each other. This gradually builds respect and then a deeper connection.
The contrast between their characters. Saber Alter is often seen as a darker, more brooding version of Saber, while Shirou is the idealistic hero. Their interactions can be really captivating.
Another plot could involve a love triangle where Shirou is caught between his feelings for Fem Gilgamesh and another character. This would add a layer of drama and conflict as he has to navigate his emotions and the complex relationship dynamics. Fem Gilgamesh, with her pride, would also have to face the idea of competing for Shirou's affection.
A plot might involve Merlin leaving Camelot to seek greater magic knowledge. He has learned a lot in Camelot, but there are still secrets about his powers and the old magic that he can't uncover there. So, he sets off into the unknown, leaving behind his friends and the life he has known. This could lead to him encountering new magical creatures and learning ancient spells that he can later use to help Camelot in a time of great need.
One interesting fanfiction could be where Saber summons Shirou in a modern setting with a twist. For example, instead of the usual Holy Grail War context, it's in a world where magic is more commonplace. Saber might summon Shirou to help her with a different kind of quest, like saving a magical artifact from being misused. The story could explore their relationship development outside of the typical war scenario.
Another interesting one is 'Under the Moonlit Alter'. This story focuses on the more emotional side of their relationship. It shows how their bond develops over time, starting from a place of mutual suspicion to a deep and abiding connection. The author does a great job of describing their internal thoughts and feelings as they navigate their relationship.