Well, a common theme is the power dynamics between them. Since Saber is a powerful Servant and Shirou is a human with his own set of skills. Fanfictions often play with how this power difference affects their relationship. It could be that Shirou has to prove himself to Saber in some way, or Saber has to learn to rely on Shirou despite her strength. Another theme is the idea of sacrifice. In the original story, there are elements of sacrifice, and fanfictions expand on this. Maybe Shirou is willing to sacrifice more for Saber's sake, or vice versa.
One popular theme is the exploration of their relationship in alternate universes. For example, in some fanfictions, they might be in a modern setting rather than the original Fate/stay night universe. Another theme could be the growth of their bond through various challenges. They might face new enemies together, which deepens their connection. Also, the theme of self - discovery within their relationship is common. As they interact more, they learn more about themselves and what they truly want from each other.
Some fanfictions focus on the cultural differences between Saber and Shirou. Saber comes from a different time and place, and this can lead to interesting scenarios. For instance, she might not understand some modern concepts that Shirou takes for granted, and they have to work through these misunderstandings. Also, the theme of redemption can be present. If either Saber or Shirou has made mistakes in the past, their relationship can be a means of finding redemption. They support each other and help each other move forward from their past wrongs.
Chapter 340, ", Fufana", is the clearest early answer because it turns Fufana's situation into a concrete plot event. It opens with That exercise, it wasn't just her from the Fufana Family who... and closes on The family was supposed to be your support, but now it seems it has.... The key payoff is that the chapter closes with Yelisia's smiled radiantly., which gives Fufana a stronger narrative position and pushes the relationship tension onward.
Chapter 389, ", Capturing Planet", is the clearest early answer because it turns Lion King Tanks's situation into a concrete plot event. The chapter turns that into something concrete by moving from However, regardless of how many are willing to buy in, the internal... to However, at the critical moment, it was the Interstellar Warriors who....
Chapter 352, ", Going Against the Current", is the clearest early answer because it turns Everyone's situation into a concrete plot event. It opens with And yet, Fino City was still advancing. and closes on Although doing this would subject them to fierce counterattacks by.... The key payoff is that the chapter closes with The newly arrived intelligence officer was a bit baffled, but with important information at hand, he hurriedly spoke up, "Commander!
Chapter 256, ", you've guessed it, right?", is the clearest early answer because it turns Nes Luman's situation into a concrete plot event. Early on, When Gu Hang received the battle report a step ahead, he knew that.... By the end, After winning the war, the Planetary Governor held a banquet to thank.... Inside the broader family politics storyline, the chapter closes with 4k, which gives Nes Luman a stronger narrative position and pushes the power growth onward.
Chapter 339, ", Fine Gold, Knight and Titan", is the clearest early answer because it turns Gu Hang's situation into a concrete plot event. Early on, He already had the name in mind, "Alliance National Knights.".... By the end, Why would that be called epic technology?.
Chapter 361, ", Invading the Divine Realm", is the clearest early answer because Ge Wajia finally turns buildup into a real advancement. It opens with The Storm God Kingdom shook violently, and even Gu Hang in the real... and closes on Not to mention, the power of that incarnation was somehow used by....
Chapter 257, ", They Struck First", is the clearest early answer because it turns Gu Hang's situation into a concrete plot event. The chapter turns that into something concrete by moving from After a pause, Wang Qi continued, "Moreover, this is just a simple... to Indeed, what would it look like to have a centralized state emerge....
Chapter 238, ", 'Unique' upgrade sequence unlocked", is the clearest early answer because Spiritual Energy finally turns buildup into a real advancement. Early on, To remain human, or to ascend to godhood?. By the end, Secondly, even if Gu Hang didn't care about "no longer being me," it.... Inside the broader faction conflict storyline, it turns Spiritual Energy's growth into a concrete upgrade step and sets up the next payoff in the power growth storyline linked to Rage Owl Star.
Chapter 264, ", Rage Owl Star Port", is the clearest early answer because it turns Star Sector Government's situation into a concrete plot event. It opens with On the return journey aboard Yelisia's starship, Gu Hang didn't... and closes on Gu Hang promised that the number of troops stationed on Heijian Star.... The key payoff is that the danger stops being abstract and the conflict around Star Sector Government becomes immediate, forcing the surrounding cast to react under pressure.
Chapter 263, ", Toiling Hard for 20 Years", is the clearest early answer because it turns Luman Kingdom's situation into a concrete plot event. The chapter turns that into something concrete by moving from After dealing with Nes Luman's affairs and securing a Puppet... to Then, an invitation arrived, requesting their presence in Pincer City....