A third plot idea might involve a young Shirou accidentally summoning Saber. Since he is a child, he doesn't fully understand the implications. Saber then has to protect him from other magical threats while also trying to figure out how to return to her own realm. During this time, Shirou shows his natural inclination towards heroism which Saber encourages.
Another interesting plot could be set in a scenario where Shirou, as a child, is sick. Saber, using her magical powers in a limited and gentle way, tries to heal him. This could lead to a deep bond forming between them as they share quiet moments during his recovery. Along the way, Shirou starts to idolize Saber even more.
One plot idea could be that child Shirou discovers Saber's true identity as a king through a magical encounter. Maybe they go on a small adventure in the local forest, with Saber teaching Shirou about honor and courage in a child - friendly way.
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.
Perhaps they face challenges from the magical world. Since Saber has a connection to the throne of heroes, there could be threats from other entities who don't want a married Saber. They would have to fight together to protect their relationship and their new life. Meanwhile, they are also growing closer and deeper in love as they face these difficulties side by side.
In fanfiction, Shirou and Saber's love is often depicted as a complex and beautiful relationship. It's a love that transcends their different natures. Shirou, with his strong sense of justice, is drawn to Saber's noble and powerful presence. Their love story can be full of moments of understanding and mutual growth.
Another plot could involve Shirou traveling to a future time where the world is in chaos due to misuse of the Grail's power. He has to find a way to reverse the damage and set things right. This would put him in a whole new set of challenges as he might face more powerful and corrupted enemies.
One plot idea could be Dark Shirou in a post - apocalyptic world where he uses his skills to survive and rule a small territory. Another could be his journey to find a way to reverse his dark transformation. Or a plot where he has to face his darker self in a psychological battle within his own mind.
One interesting plot idea could be that when Shirou summons Merlin, Merlin initially seems uninterested in the Grail War but gradually gets involved to protect Shirou. He could use his magic to deceive the other Servants, creating illusions to mislead them about Shirou's true strength and intentions.
One plot idea could be Shirou Emiya finding himself in the world of Fairy Tail and having to adapt to the magic - based society. He might try to use his Reality Marble in unique ways to combat the dark guilds. Another could be him teaming up with Natsu and his friends to take on a powerful, otherworldly threat that has somehow entered the Fairy Tail universe. He could also learn new forms of magic from the wizards in Fairy Tail, like learning how to incorporate Fairy Tail - style elemental magic into his existing abilities.
Another plot could be that Shirou discovers a new, highly competitive gamer community. He starts from the bottom but his determination and strategic thinking, which he has from his heroic deeds, help him rise through the ranks. He might make new friends and rivals in this community.
One idea could be Shirou trying to learn the ways of chivalry from Arthoria. He might struggle to adapt to the different moral and ethical codes of that time. Another could be Shirou using his modern knowledge to help Arthoria in battles, like devising new strategies.
Another plot could involve Shirou reincarnated in a modern superhero world. He might struggle to fit in at first, but then realizes his abilities can be used to fight super - villains. His noble phantasm could be adapted in a unique way to combat the new threats in this world.