One possible storyline could be a quest where the three of them have to work together to defeat a powerful dark wizard. Natsu's brute strength, Erza's strategic combat skills, and Mirajane's shape - shifting abilities would make for an amazing team. They could start off with some initial bickering due to their different personalities but gradually grow to respect and rely on each other more as the adventure progresses.
Maybe a story where they get trapped in a magical realm. Natsu tries to find a way out using his fire magic to break through any barriers. Erza keeps everyone in line and formulates plans to survive and escape. Mirajane uses her charm to gather information from the strange creatures in the realm. As they face various challenges together, their relationships deepen and a romantic triangle could start to form in a very interesting way.
A fanfiction could center around a festival in Magnolia. Natsu enters a fighting competition, Erza is one of the judges, and Mirajane is helping with the food stalls. Natsu's over - the - top performance in the competition catches both Erza's and Mirajane's attention. Erza has to maintain her composure as a judge while secretly being impressed. Mirajane teases Natsu about his performance later. This could lead to a series of events that bring the three closer together in unexpected ways.
One idea could be a story where they go on a quest together. Maybe they have to find a rare magical item. Natsu's impulsiveness, Mirajane's charm, and Erza's strict leadership combine in interesting ways during the adventure.
One popular storyline could be them going on a dangerous mission together. Mirajane's powerful magic and Natsu's dragon - slayer abilities would make for an exciting adventure. They might face a powerful dark guild and have to rely on each other to survive.
One great storyline could be Natsu and Erza having to protect their family from a powerful dark guild. They'd use their combined magic and teamwork to fend off the threats. Another could be them raising a young child with special powers within their family, teaching the child about love and friendship just like they've learned in Fairy Tail.
There might be a fanfiction where they participate in a guild - wide competition. Natsu would be all about winning, Erza would be determined to show her strength and uphold her honor, and Mirajane would be there with her own set of skills. In the story, they could form an unexpected alliance with other guild members and through teamwork, overcome challenges and rivals.
A common type of fanfiction might be a love story between them. Despite their different personalities, they could gradually fall in love. For example, during a long and dangerous quest, they start to see each other in a new light. Or perhaps a story where Mirajane's past traumas are revealed to Natsu, and he helps her overcome them, strengthening their bond in the process.
Perhaps the OC is from a different dimension where magic works in a strange way. Natsu, Mirajane, and Erza are intrigued by this. They team up to help the OC understand and control their magic in the world they are in now. Along the way, they encounter a powerful dark wizard who wants to use the OC's unique magic for evil. So, they have to fight together to protect the OC and the world from this threat.
One great story could be 'Natsu and Mirajane's Adventure'. In this fic, they might go on a quest together, facing various challenges that test their relationship and individual strengths. It could involve them using their magic in creative ways to overcome obstacles.
One unique way to develop their relationship could be through a shared loss. For example, if a beloved member of the guild was killed. Natsu might react impulsively with anger, Erza would be more stoic but determined for justice, and Mirajane would be the one to comfort them both while also being sad herself. This common grief could bring them closer together, with Natsu realizing he can rely on the two women in different ways. Erza could see Natsu's softer side and Mirajane could see a new depth to Erza.
One great fanfic could be 'The Adventure of Natsu and Erza'. It focuses on their unique bond during a dangerous mission. They rely on each other's strengths and in the process, their relationship deepens in a very platonic yet heartwarming way.
Their personalities. Natsu is the hot - headed and impulsive one, always ready to jump into action. Erza is the strict and disciplined warrior, bringing order and strategy. Mirajane is the more laid - back but still very powerful one. Together, they create a great balance.