A common theme is adventure. Since Kirito is known for his adventures in the virtual world, these fanfictions often have the reader joining him on exciting quests. Another theme is romance, of course, showing the relationship between Kirito and the reader.
One frequent theme is self - discovery. The reader, in the presence of Kirito, often discovers new aspects of themselves. Also, the theme of friendship is there. Even though it's a kirito x reader, there are usually other friends around, and the story shows how they all interact. For example, in some fanfictions, they team up with other characters from the original series to face big challenges.
Friendship is a common theme. Their bond as comrades in the virtual world is often explored, like how they trust and depend on each other in battles.
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.
One common theme is the exploration of gender - reversed dynamics. Since Kirito is usually male in the original, seeing how a female Kirito interacts with Asuna brings a fresh perspective. Another theme is the strengthening of their bond. These fanfictions often focus on how their relationship grows deeper in different situations.
Another theme is the discovery of self - worth through love. The oc characters often start out with insecurities or a sense of not belonging. But through their relationship with Kirito, they learn to value themselves more. For example, an oc might think she's not strong enough in the game, but Kirito makes her see her own unique qualities.
A frequent theme in these fanfictions is the exploration of new identities. Kirito, being in a different world, has to re - define himself, and the Fate characters also see him in a new light. Teamwork is another big theme. They have to work together to face the challenges of the Grail War or other threats in the Fate world. And of course, the theme of heroism. Kirito's heroic nature from Sword Art Online and the heroic ideals in Fate/stay night are often compared and combined in these stories. For example, in some fanfictions, Kirito takes on the role of a hero in the Grail War, much like the Servants in Fate/stay night.
Love and friendship are common themes. Many fanfics explore how their friendship could potentially turn into a deeper romantic relationship, like in 'Kirito and Lizbeth: The Unspoken Love'.
The theme of self - discovery also pops up. As they interact with each other in the fanfics, they often discover new things about themselves, like hidden strengths or weaknesses, which in turn affects their relationship.
Another theme is adventure. Since they are in a virtual world, they often go on quests together. Fanfics will describe their adventures, like exploring new areas, fighting powerful enemies, and solving mysteries along the way.
The theme of growth, both for Kirito and the girls in the harem, is often seen. Kirito may grow as a person in terms of his ability to handle multiple relationships, and the girls may grow in their confidence and abilities as they are part of Kirito's life. Also, the concept of loyalty within the harem is a common theme, with the girls showing loyalty to Kirito and also to each other in some cases.
One common theme is adventure. Since they are from the Sword Art Online universe, they often go on quests together in fanfics. Another theme is love, as their relationship is a central focus. It can range from a budding romance to a deep and abiding love.