In my opinion, they're both great in their own ways. The story of Xenoblade Chronicles 1 was classic and engaging, while Xenoblade Chronicles 2 has its own unique charm and depth.
Well, in a Brianna and Fiora story romance novel, perhaps Brianna is a shy girl and Fiora is a more outgoing one. They could be from different social backgrounds. Maybe Fiora helps Brianna break out of her shell, and as they spend more time together, feelings start to develop. They might go on adventures, discover new things about each other, and their love story unfolds against a backdrop of beautiful settings and interesting events.
The theme of self - discovery is also quite common. Through their relationship, both Fiora and Riven may learn more about themselves. In some fanfics, Fiora discovers a new side of herself as she gets to know Riven better. And Riven may come to terms with her past and her identity through her bond with Fiora.
The plot might involve Aatrox being intrigued by Fiora's unwavering courage. He could see in her a potential to be a great warrior on his side, not as a minion but as an equal. So he tries to persuade her to join his cause, which leads to a series of intense dialogues and battles between them, as Fiora is hesitant but also curious about Aatrox's power.
One common theme is friendship. Just like in the game, fanfics often explore the deep bonds between the characters. For example, the relationship between Rex and his Blades is further developed in many fanfics.
The story length of Xenoblade Chronicles can vary depending on how much side content you explore. On average, it takes around 50 to 80 hours to complete the main story.