One interesting fanfiction could be about the male spirit having to adapt to the human world in a unique way. Maybe he has to deal with modern technology that is completely foreign to him, like trying to figure out how a smartphone works while also hiding his true identity from the other characters.
There are many interesting stories. For example, the interactions between the main characters and the Spirits are quite engaging. Each Spirit has her own unique personality and backstory, which makes the short stories full of surprises.
Some writers might be known within the Date A Live fan community. You could try joining some fan groups on social media platforms and ask for recommendations. They might point you to writers who have a unique take on the male spirit characters, whether it's making them more heroic or exploring their more vulnerable sides.
Another interesting OC could be a spirit who has the ability to communicate with animals. This OC could bring a whole new dynamic to the story as she tries to understand the human world through the eyes of the animals she befriends. She might also use her animal friends to help Shido in his missions, like having birds spy on the AST or something.
One idea could be that the main character has memories of their past lives and uses that knowledge to change the fates of the Spirits in a more positive way. For example, they might be able to prevent some of the more tragic events that usually occur in the original story.
The plot twists in the Date A Live light novels are quite something. It's not just about the protagonist, Shido, sealing the spirits. There are deeper conspiracies and relationships that unfold as the story progresses. The way the different timelines and alternate universes are sometimes hinted at adds an extra layer of mystery.
In a Naruto x Date A Live fanfiction, a great crossover would be in terms of combat strategies. The Date A Live characters are used to dealing with spirits in their own ways, but Naruto characters bring in a whole new level of combat knowledge. The Date A Live crew could learn about teamwork from Naruto's team formations. Also, the different elemental jutsus from Naruto could be incorporated into the Date A Live world, like using fire jutsu to fight against a particularly powerful spirit.
One idea could be that the protagonist travels back in time to prevent a certain spirit from becoming a threat in the first place. Maybe they change a key event in the spirit's past that alters their future path.
A plot idea could be that a powerful Spirit in Date A Live is somehow transported to the Naruto world. This Spirit's power causes chaos, and Naruto and his friends have to figure out how to send it back. Along the way, they discover that the Spirit has a tragic past similar to some of the characters in Naruto. This leads to an unexpected bond between them.
In a 'Naruto in Date A Live' fanfiction, Naruto could be a key figure in preventing a total war between the Spirits and humans. His ability to understand and empathize with outcasts (like he did with Gaara) could help him communicate with the Spirits on a deeper level. He could teach Shido some of his ninja techniques to better protect the Spirits and also use his own chakra to help stabilize the space - quakes caused by the Spirits, thus bringing a new hope for peace in the Date A Live world.
The Date A Live Visual Novels have a really immersive world - building aspect. The setting where the spirits exist and interact with the human world is well - crafted. It has its own rules and mysteries. The music in the visual novels also sets the mood really well, whether it's a tense battle scene or a romantic moment. Additionally, the decision - making system in the game is not too complex but still allows for enough variety in the story to keep players interested.