One idea could be that a shy girl who loves art has a secret admirer who leaves little sketches in her locker. Turns out it's the popular jock who is also an artist but doesn't want to show it because it doesn't fit his 'tough' image. Eventually, they bond over their shared passion for art and start a sweet romance.
One idea could be that Naruto characters are transported into the Dark Souls 3 world. For example, Naruto with his high energy and determination could be seen as a sort of chosen undead. He might use his shadow clones in a unique way to fight the various demons and bosses in the game world. His chakra could be translated into a form of 'soul energy' in the Dark Souls 3 context.
One idea could be that Bloom discovers a hidden form of dark magic within her powers. She has to struggle to control it and not let it corrupt her, while her friends in Winx are both afraid and determined to help her. Maybe she meets an ancient being who knows about this type of dark magic and she has to make a deal with it to understand it better.
Perhaps a story where Dark Sonic is being chased by some dark forces and he hides in Rainbow Dash's cloud home. Rainbow Dash discovers him and at first is scared but then decides to help him. Together, they fight off the dark forces, with Rainbow Dash teaching Dark Sonic about friendship and loyalty along the way.
A cool idea for a Dark Shadow fanfiction could be a story where Dark Shadow gets separated from Tokoyami and has to find its way back. During this journey, it discovers things about itself and the world that it never knew before.
A girl who is really into music and plays in the school band falls for the boy who is always at the back of the auditorium listening to them practice. He has a crush on her too but is too shy to say anything. One day, she loses her sheet music and he finds it and returns it to her. This starts a conversation and they realize they have a lot in common, like their love for a particular genre of music. So they start dating and going to concerts together.
A great dark romance story often has complex characters. For example, if the characters have deep - seated issues like past traumas or inner demons, it adds to the 'dark' aspect. In 'The Phantom of the Opera', Erik, the Phantom, has a tortured soul because of his disfigurement, and his love for Christine is both passionate and dangerous.
One idea could be a group of acolytes investigating a cult that seems to be summoning daemons in an abandoned cathedral. They have to navigate through the dark and spooky corridors, facing traps and possessed cultists.
A fanfic about a group of adventurers teaming up to take on the Capra Demon in a completely different way than in the game. For example, instead of fighting it head - on, they use their wits and the environment to outsmart it, like luring it into a trap.
Another approach could be to merge the magic systems. In Dark Souls, there are different types of magic like pyromancy and sorcery. Imagine if these were introduced into the Game of Thrones world. Maybe a pyromancer could influence the outcome of battles in Westeros in a new and unexpected way, or a sorcerer could use their illusions to deceive the power - hungry lords and ladies.