Well, Bruno is quite popular. His mysterious nature and his relationship with Yusei can bring an interesting dynamic. And then there's Kalin Kessler. His backstory as a former Dark Signer can be explored further in relation to Yusei. Luna and Leo also get included sometimes as they are part of the overall story and can interact with Yusei in unique ways.
Crow Hogan is often a popular character to include. He's Yusei's friend and his presence can add more depth to the story. Another one could be Jack Atlas. His rivalry with Yusei and his strong personality make him a great addition. Also, Akiza Izinski might be included as she has her own powers and a connection to Yusei.
Some common themes in Dark Signer Yusei fanfiction could be redemption. Since the Dark Signers are often seen as antagonists, fanfics might explore their journey towards redemption. Another theme could be power struggles. Yusei, being a powerful duelist, might face intense power battles against the Dark Signers in these stories. Also, friendship can be a theme as Yusei tries to understand the Dark Signers and maybe even form an unlikely bond with them.
In a 'yusei becomes dark signer fanfiction', perhaps Yusei discovers a hidden part of his past that links him to the Dark Signers. He could find out that his family was somehow involved with the dark forces in the past. This revelation shakes his sense of self. As a result, he decides to embrace the role of a Dark Signer to fully understand his heritage. However, he soon realizes that the power comes with a price, and he has to fight against the corrupting influence of the dark energy while still trying to achieve his own goals.
Romantic relationships would also be affected. If Yusei had a love interest, she or he would be heartbroken and confused. They might try to reach out to Yusei and bring him back from the dark side. But Yusei, as a Dark Signer, might push them away, believing that his new path is one he has to walk alone. His relationships with his mentors or older figures in his life would also turn sour, as they would see him as having strayed from the right path.
He could interact with the main characters from Duel Academy like Jaden. They might have some exciting duels together.
A really interesting fanfiction I came across was about Yusei's encounters with other Dark Signers before fully becoming one himself. It showed how he was gradually influenced by the dark forces. In some fanfictions, the author might focus on Yusei's new deck as a Dark Signer. It could have cards with darker themes and more powerful but dangerous effects. These fanfictions can offer a different perspective on Yusei's character compared to the original series.
Some of the most popular Dark Signer OCs are those that have a connection to the existing Yugioh 5ds lore in a new and unexpected way. For instance, an OC who is related to one of the ancient dragons in the series but has become a Dark Signer. They bring a fresh perspective to the story, as readers are curious to see how this new element will interact with the established plotlines and characters.
You can start by looking on fanfiction websites like FanFiction.net or Archive of Our Own (AO3). These platforms have a large collection of Yu - Gi - Oh fanfictions, and you can specifically search for ones related to Dark Signer Yusei.
Together, they could bring out different sides of each other. Yugi might make Yusei more open - minded about the spiritual side of dueling, while Yusei could teach Yugi some practical skills like how to better maintain his cards or build a more efficient deck. Their combined traits would make for an exciting dynamic in the fanfiction.
One of the most popular characters to include is the outcast. This character is already on the fringes of society and may have a special connection to the whispers because of it. They could be seen as an outsider looking in on the normal world that is being disrupted by the whispers. Another great character is the wise elder, who has heard tales of the whispers in their youth and can offer valuable advice. And a character with psychic abilities who can communicate with the source of the whispers in a different way than the others can also be very interesting to write about.
Harvey Dent, or Two - Face, is another favorite. His fall from grace and his split - personality concept offer a lot of room for exploration. Fanfiction can delve into his recovery attempts or his further descent into villainy.