Romance is of course a big theme. There could be slow - burn romances where the relationship builds up over time. There might also be themes related to the world they live in, like dealing with the politics or magic systems of their fictional world while their relationship blossoms.
One common theme is possessiveness. Yuno, being a yandere, is often extremely possessive of the male reader. For example, she might get jealous easily if the male reader so much as talks to another character.
One common theme is mystery. Since both characters have their own secrets, fanfics often explore how they discover each other's hidden sides. Another theme is loyalty, as they might show loyalty to each other in different situations.
One common theme is the protection of the male reader by Yuno. Given Yuno's possessive nature in the original story, in fanfictions she often goes to great lengths to keep the male reader safe from any threats.
Another theme is often about self - discovery. As the male reader gets involved with Koneko, he may discover new aspects of himself. And for Koneko, she might also grow in different ways through the relationship.
Another theme could be the exploration of different powers. The male reader might have some unique abilities that interact with Mercy's healing and resurrection powers in interesting ways. For example, his power could enhance her healing range or something like that. It makes for an exciting dynamic in the story.
Well, a major theme is the power of attraction. The male reader usually has some qualities that attract the female characters to him, like kindness, courage, or a special ability. Another theme is the exploration of different personalities. Each female in the harem has her own distinct personality, and the male reader has to understand and deal with them all. And, of course, there's the theme of love and loyalty. The relationships in the harem are often based on some level of love and loyalty among the characters.
One common theme is adventure. Since Carmelita is often associated with action - packed scenarios in the Sly Cooper universe, the fanfic might involve the male reader and Carmelita going on some exciting adventures together.
One common theme is adventure. The story might involve the male reader and the mania character going on an exciting journey together, facing challenges and solving mysteries.
A common theme is friendship. The male reader and Sol often start as strangers and develop a deep friendship over time. Another theme could be adventure, as they might go on quests or explore new places together.
Friendship is also a big theme. The male reader forms bonds with the Avengers members, like a brotherly bond with Thor or a mentorship - like relationship with Iron Man. These relationships are explored in different ways in various fanfics, sometimes with humor and sometimes with more serious emotional depth.