Lucy would be an interesting choice. She could provide a different perspective as a celestial wizard. Her kind nature might also help in bringing out different sides of Sting and Rogue, and she could use her magic to assist them in their adventures or battles.
Natsu could be a great character to pair them with. Since he's also a dragon slayer, there could be some interesting interactions and competitions among them. They could learn from each other's dragon slayer techniques.
Natsu could be a great character to pair them with. Natsu's fiery and impulsive nature would contrast well with Lucy's more level - headed and Erza's strict personality. They could all go on an adventure together, with Natsu leading the charge into dangerous situations, Lucy using her celestial spirits for support, and Erza keeping them in line. Gray is also a good option. His cool - headedness and ice - make magic could add an interesting dynamic to the group, especially when paired with Natsu's fire magic and the celestial and re - equip magic of Lucy and Erza.
In a crossover with 'One Piece', they could be paired with Luffy. Luffy's carefree and determined nature would contrast well with Freed and Laxus. They could all be on a quest to find a magical treasure that has power over both their worlds. Luffy's Gum - Gum powers would be interesting to see alongside Freed's rune magic and Laxus' lightning.
Some characters like Natsu might be initially suspicious. He's always been competitive with Sting, so he might think they have some ulterior motives. But characters like Lucy would probably be more welcoming. She's always open - minded and would see it as an opportunity to make new friends. Happy would also be curious and might follow them around to see what they're up to.
For Lucy, you could develop her character by showing her growing more confident in her magic. Maybe she starts to experiment with new ways to summon her Celestial Spirits or combines their powers in unique ways. With Sting, you can explore his past more deeply. Show how his experiences as a Dragon Slayer have shaped his personality, and have him face some internal conflicts related to his power and identity. As for Rogue, you could develop his relationship with his shadow. Maybe he discovers new abilities within his shadow magic. Also, in the fanfiction, put them all in situations that force them to interact and grow together. For example, a mission where they have to protect a village from a powerful dark mage.
Another common theme is power and growth. Writers often show how Rogue and Sting become stronger over time. For example, they might face a powerful enemy and through that experience, they learn new magic or improve their existing skills. It's about their journey to become more powerful dragonslayers.
Kirby and Natsu would make a great pair. Natsu's fire - based magic and Kirby's ability to absorb and copy abilities could create some really cool combat combinations. They could both be hot - headed in their own ways and charge into battles without much hesitation.
Juvia is an obvious choice. Their relationship in the original series is full of interesting dynamics. Juvia's over - the - top love for Gray can lead to many comical and heartwarming situations in fanfiction. Another good option is Natsu. Their friendly rivalry can be explored further, like having them team up against a powerful enemy they couldn't defeat alone.
Lucy would also be a good pairing. She's intelligent and has a wide range of celestial spirits at her disposal. Sora could learn a lot from her about magic, and together they could use their different skills to solve mysteries or defeat enemies. Maybe Sora has some knowledge about the celestial world that Lucy doesn't, and they can share and grow together.
Natsu could be a great character to pair with Kinana. He's adventurous and his warm personality could bring out different sides of Kinana. Also, Gray would be an interesting choice. His cool and sometimes aloof nature could contrast well with Kinana's more reserved self. And Erza, with her strong leadership and warrior spirit, could form a great partnership with Kinana in a fanfiction, perhaps teaching her some combat skills.
For Lucy, you could explore her celestial spirit powers more deeply. Maybe she discovers a new and rare spirit that has a special connection to Rogue or Sting's magic. For Rogue, his relationship with his shadow could be further developed. He might learn to use his shadow in new ways, and Lucy and Sting could play a role in that discovery. For Sting, his leadership skills could be tested and improved. They could be put in a situation where Sting has to lead a group that includes Lucy and Rogue, and he has to make tough decisions.