It could develop in a rather unexpected way. Suppose there's a magical accident that causes their minds to be linked for a short time. They get to see each other's deepest fears and desires. This experience could make them more empathetic towards each other. After that, Mystogan might be more protective of Wendy, and Wendy could be more understanding of Mystogan's often - mysterious ways. Their relationship could then evolve from a simple acquaintance in the guild to a pair that has a special connection that is unique to them.
At first, their relationship might be one of mutual curiosity. Naruto would be intrigued by Wendy's magic, and Wendy would be fascinated by Naruto's ninja abilities. As they face challenges together, they would start to trust each other more. For example, if they are in a battle against a strong enemy, Naruto would rely on Wendy to back him up with her support magic, and Wendy would depend on Naruto's combat skills.
If in an alternate universe, Mystogan was raised in a different guild and Natsu was sent to bring him back to Fairy Tail. Natsu would initially be frustrated with Mystogan's aloofness. However, as they travel together, Natsu would learn about Mystogan's past and the reasons for his detachment. This understanding could lead to a friendship developing between them, and in the end, Mystogan might decide to join Fairy Tail because of Natsu's influence.
In a fan - made story, their relationship could develop through shared goals. For example, if there is a threat to the Fairy Tail world that only their combined powers can stop. As they work together towards this goal, they start to understand each other better. Zeref might be softened by Lucy's optimism and determination, and Lucy might see the good in Zeref that is buried deep beneath his dark exterior. This could lead to a relationship filled with mutual respect and love over time.
Their relationship might develop in a more emotional way. Maybe one of them gets injured during a battle, and the other is extremely worried. This concern could make them realize how much they care for each other. They could then start to open up about their fears and dreams, which would bring them closer together. They might also discover that they have a lot in common in terms of their goals within the Fairy Tail guild.
Their relationship could develop through training sessions. As they train together, they learn more about each other's strengths and weaknesses, and a bond of mutual respect forms.
There could be a fanfiction where Mystogan has a premonition about a future threat to Wendy. He then decides to secretly protect her. Along the way, Wendy discovers what he's doing and they have a heart - to - heart. This could lead to a development of romantic feelings between them, or at least a very strong platonic bond as they face the impending danger together.
In many fanfictions, Wendy and Lucy's relationship is developed when they help each other with their magical training. Wendy might teach Lucy about some of her unique dragon - slayer magic techniques, and Lucy could share her celestial spirit knowledge with Wendy. As they learn from each other, they become closer. Also, there could be situations where they protect each other from the judgment or jealousy of other guild members, which cements their relationship further.
Natsu would likely become more responsible. He might start to take on more jobs around the guild to earn extra money for the future of his family. His carefree attitude would be tempered with a sense of duty. Wendy would develop a stronger sense of self - worth. In the past, she may have felt like she was just a young and inexperienced member of the guild. But now, with a new life growing inside her, she realizes her importance not just as a dragon slayer but as a mother - to - be. This new - found self - worth would make her stand taller and be more vocal in the guild, advocating for herself and her unborn child.
Well, it could develop in a really comical way. Imagine Tatsumaki trying to teach Saitama some 'proper' hero etiquette, but Saitama just doesn't get it. However, through these interactions, they start to understand each other better. Tatsumaki sees Saitama's kindness and Saitama sees Tatsumaki's determination. This mutual understanding could lead to a unique relationship in the fanfiction.
Their relationship could develop through mutual respect for each other's strength. Natsu is a powerful wizard in Fairy Tail, and Kagura is no less in her own guild. When they first meet in battle or some other situation, they recognize the power in each other, which could be the start of a relationship where they gradually become friends.