The plot could be centered around a mysterious magical anomaly that Artoria can't handle alone. So she summons Archer Emiya. They then embark on a journey to figure out the source of the anomaly. During this journey, they face many challenges that test their skills and their relationship. Eventually, they succeed in solving the mystery and in the process, become closer as comrades.
A possible plot is that Artoria summons Archer Emiya to assist in a war against a powerful dark force. Emiya brings his strategic mind and combat skills. At first, Artoria's knights are skeptical of this new summoned hero. But as Emiya proves himself in battles, they start to accept him. The two main characters have to deal with not only the external enemy but also internal politics within Artoria's camp. Their relationship evolves from a simple master - servant one to a deep friendship as they fight side by side.
Well, it could start with Artoria having a premonition of a great disaster. She decides to summon a hero who can help prevent it, and that hero is Archer Emiya. Once summoned, they find that the disaster is part of a much larger, complex plot involving different factions and powerful magic. They have to navigate through a web of lies and deception. Emiya uses his knowledge of modern tactics and his sharp senses, while Artoria uses her ancient wisdom and strong leadership. As they progress, they start to understand each other's motives and values better, and together they work towards stopping the impending disaster.