Joker is often paired with the female protagonist. Their relationship can be explored in different ways, from being comrades in the Phantom Thieves to having a more romantic connection. Ryuji is also a popular choice as they can have a fun, energetic dynamic.
Yosuke is often paired with the female protagonist. Their dynamic, which can range from friendly banter to a deeper connection, makes for interesting fanfic scenarios.
The Medic can also be paired with the female spy in fanfiction. The Medic's ability to heal and the spy's ability to infiltrate can make for some great stories. For instance, the spy might be on a mission where she gets injured and has to rely on the Medic to patch her up while still keeping their location a secret from the enemy. This creates a lot of tension and opportunities for character development in the fanfiction.
Shampoo is also a popular character to be paired with Ranma in such fanfictions. Given their complex relationship in the original series, when Ranma stays female, it can lead to some really unique and engaging storylines. There are also some fanfictions where Ranma gets paired with new characters introduced specifically for the fan - created story.
In many Hogwarts female Rowan fanfictions, Ben Copper is often paired with Rowan. They have a great dynamic where Ben's cautious nature contrasts with Rowan's more adventurous side. Another popular pairing is with Penny Haywood. Their friendship can easily turn into something more in fanfictions, as Penny's charm and Rowan's intelligence complement each other.
Hermione is often paired with female Harry in a strong friendship way. They can support each other through all the challenges at Hogwarts. Ron can also be part of their group, and there might be a more platonic relationship between female Harry and Ron. Dumbledore is always an important character in relation to female Harry, guiding her and protecting her as he did with male Harry.
Sakura is often paired with Naruto in such fanfictions. Since she already has a complex relationship with Naruto in the original series, adding the element of the female shadow clone can create interesting dynamics. For example, the clone might make Sakura see Naruto in a new light or cause some jealousy.
Cthulhu is often paired with Nyarlathotep. Since they are both from the Lovecraftian mythos, their combined presence can create a much darker and more chaotic story. Another character could be Sherlock Holmes. The contrast between Holmes' rational mind and Nyarlathotep's otherworldly chaos makes for an interesting dynamic. Holmes would try to solve the mystery of Nyarlathotep's appearance and actions, while Nyarlathotep would be constantly trying to undermine Holmes' sanity.
Zoro is another popular character. He and Luffy have a strong bond, and in Gear 5 fanfiction, they might fight together in a new and more coordinated way. Zoro could be using his swordsmanship to complement Luffy's wild and unpredictable Gear 5 attacks, creating a powerful combination against their enemies.
Alice Angel is often paired with Baby Bendy. Their interactions can range from her being a sort of mother figure to him, guiding him through the dark and twisted world, to more complex relationships where they might have conflicting goals but still a connection.
Another popular character to be paired with the 'brother of Naruto' is Hinata. The brother could be protective of Hinata's relationship with Naruto or he could develop his own feelings for her, creating a love triangle situation which adds a whole new layer of drama to the fanfiction.