Inosuke is interesting as well. He was raised by wild boars and has a very wild and unruly nature. He is extremely competitive and has his own strange ways of fighting demons. His rough exterior but good heart make him a memorable character.
Zenitsu is quite interesting. His cowardly nature at first, which is in contrast to his amazing lightning - based fighting skills when he's unconscious, creates a lot of comical and engaging moments in the light novel. Inosuke is also fascinating with his wild and boar - headed appearance and his brute - force fighting style.
One popular trope is the 'power - up' trope. In many fanfictions, characters from both Fairy Tail and Demon Slayer gain new powers or improve their existing ones in unique ways. For example, a fanfiction might have Tanjiro learning some Fairy Tail magic to enhance his demon - slaying abilities. Another common trope is the 'team - up' trope. Fans love to see characters like Natsu and Tanjiro working together against a common foe. It creates a lot of exciting action scenes and interesting character dynamics.
A common theme is power - up. Writers like to show Gray getting new powers related to demon slaying and how he masters them. For example, in some fanfics, he gains a new form of ice - make magic that can harm demons more effectively.
In Naruto fanfiction, a popular theme is power - ups. Fans like to write about Naruto or other characters getting new and stronger abilities. For Demon Slayer, the theme of redemption for demons is quite common. In Fairy Tail, friendship and the power of the guild are often - explored themes. For instance, many Fairy Tail fanfictions show how the strong bond between guild members helps them overcome difficulties.
A popular theme is the power - up theme. Lucy might gain new powers related to Demon Slayer abilities in the fanfiction. For instance, she could develop a way to use her magic to purify demons like the Demon Slayers do with their swords.
Naruto himself is often a popular character in these fanfictions. Writers like to put him in situations where he teams up with the Phoenix Slayer. Another popular character could be Sasuke. His brooding nature and powerful abilities make for interesting interactions with the Phoenix Slayer concept. Also, Kakashi is often included as he is a fan - favorite and his wisdom can add depth to the story when dealing with the new element of the Phoenix Slayer.
Buffy herself is often a very popular character in Wishverse fanfic. Writers like to explore different versions of her, like a more jaded Buffy in a darker Wishverse. Spike is also popular as his complex character can be taken in many new directions in the alternate reality. And Willow, given her powerful magic, can have some really interesting storylines in the Wishverse.
Jack himself is obviously a very popular character to include. He's the hero of the story, so most fanfictions would center around him in some way. The princess is also a popular choice. Writers can explore her relationship with Jack further, like how she helps him in battles or how their relationship develops after the main events of the story. And of course, the giants can be great characters to include. You can create different personalities for them, like a giant who is more intelligent and cunning than the others.