Yes, there are quite a few. You can start by looking on popular fanfiction websites like FanFiction.net or Archive of Our Own. Just search for 'Sachi x Kirito' and you'll find a variety of stories, ranging from romantic ones to more adventure - centered tales that also explore their relationship.
There are several common themes. First, there's the theme of unrequited love or the slow - burn romance. Sometimes Sachi has feelings for Kirito that she's afraid to show, or it takes a long time for them to realize their feelings for each other. Second, there's the theme of sacrifice. Sachi might be put in a situation where she has to sacrifice something for Kirito, or vice versa, which tests and deepens their relationship. And of course, the theme of adventure is also common as they are in a virtual world full of quests and challenges that they face together.
I really like the fanfic 'Sachi's Legacy'. In this one, Sachi's impact on Kirito is explored in depth. It shows how her memory stays with Kirito even after she's gone and how it influences his actions and decisions throughout the story. It's a very emotional read.
You can try some popular fanfiction websites such as Archive of Our Own (AO3). It has a large collection of fanfictions from various fandoms, including Sword Art Online where Kirito and Sachi are from. There are usually good search functions on these sites that allow you to specifically look for kirito x sachi fanfiction.
One great kirito x sachi fanfiction could be 'The Lost Memories of Sachi'. It delves into what could have happened if Sachi's memories were somehow restored and how her relationship with Kirito would develop. Another one might be 'Sachi's Second Chance' which gives Sachi a new opportunity to be with Kirito in a different virtual world setting.
You can start by looking on fanfiction.net. It has a large collection of Sword Art Online fanfics, and there are likely quite a few Kirito x Sachi ones there. Just use the search function and type in 'Kirito x Sachi' and you should find some interesting reads.
I'm not entirely sure as I haven't read this specific web novel in detail. But generally, it might involve the relationship between Kirito and Sachi, perhaps their adventures together in a virtual world, facing challenges and growing as characters.
Yes, on AO3 there are some highly rated ones. One that comes to mind often has a very emotional take on their relationship, exploring how Sachi's memory impacts Kirito's feelings. But it's hard to name just one as there are quite a few good ones.
Kirito and Sachi are the main characters. Kirito is likely to be a strong and resourceful character. Sachi, on the other hand, might have her own charm and role. Their interactions and the development of their relationship are probably central to the story.
Another option could be Wattpad. Although it has a wide variety of content, you can search specifically for Sachi and Kirito love story fanfictions. However, the quality may vary, so you'll need to browse through a bit to find the good ones.