One idea could be that Natsu is betrayed by his closest friends in the guild, and in his time of despair, a group of female characters form a harem around him to help him heal and regain his confidence. For example, Lucy could be the first to reach out, using her celestial magic to show him there are still things to fight for. Another plot could involve Natsu being betrayed by a powerful dark mage who manipulates his guild against him. The harem, which might include Erza, Wendy, and others, then trains Natsu in secret to become stronger and take revenge on those who wronged him.
Well, perhaps Natsu is betrayed by someone he trusts deeply, like a mentor figure. This makes him question his own judgment and his place in the world. The harem aspect could come in when different female characters from various places start to be drawn to him because they sense his pain and his pure heart. They could each offer him different things, like Levy offering her intelligence to help him figure out the truth behind the betrayal, and Juvia using her water magic to soothe his troubled mind.
A possible plot for a 'Betrayed Natsu X Harem Fanfiction' is that Natsu is wrongly accused of a crime by someone within the guild and is shunned. The harem forms as the female characters see the injustice. Mirajane could use her transformation magic to protect Natsu from any harm that might come his way during this tough time. Meanwhile, the other members of the harem like Cana might use her card magic to try and find clues to prove Natsu's innocence. As they work together, Natsu starts to develop deeper relationships with each of them.
Well, Mirajane could be part of the harem. She has a motherly side and would want to comfort Natsu if he was betrayed. Levy is also smart and resourceful, and she could use her skills to help Natsu out. Juvia, with her obsessive love for Gray, might transfer some of that intense loyalty to Natsu if she saw him in a desperate situation after being betrayed.
One interesting plot idea could be Natsu going on a special quest with each member of his harem separately. This would allow for character development of both Natsu and the individual harem members. For example, when he's with Lucy, they could discover a new type of celestial spirit magic that only works in a specific, long - lost realm. Another idea is that an enemy targets Natsu's harem to get to him, so he has to protect them all while also dealing with his growing feelings for each of them.
One idea could be that Natsu and Mirajane start a family in a peaceful post - guild - war era. Their kids inherit unique magical abilities from both of them and they have to train and guide their children through the magical world's challenges.
One idea could be Naruto somehow finds himself in a situation where he has to team up with Tayuya frequently. As they interact more, a harem starts to form around Naruto, with Tayuya being one of the key members. The plot could involve them going on missions together and Naruto gradually realizing his feelings for Tayuya among the others in the harem.
One plot idea could be that Juvia and Natsu are forced to team up on a mission in a dangerous, enchanted forest. Along the way, Juvia's feelings for Gray start to shift towards Natsu as she sees his determination and kindness in a new light. Another could be a body - swap situation where Juvia and Natsu swap bodies and have to learn to deal with each other's powers and personalities, leading to some comical and heartwarming moments. A third idea is that in an alternate universe, Juvia and Natsu are childhood friends, and they have to face the challenges of growing up and protecting their world together, with their relationship evolving from friendship to something more romantic.
Well, a plot could revolve around a competition in the Fairy Tail guild where Millianna and Natsu are teamed up. At first, they don't get along well because of their different personalities. Millianna is more sly and Natsu is brash. But as they face challenges in the competition, they start to understand each other better. Maybe there's a task where they have to rescue a group of kittens, which plays to Millianna's love for cats. Natsu, on the other hand, has to use his strength to fight off the bad guys who are trying to stop them. In the end, they become closer friends and realize they make a great team.
One idea could be that they go on a quest together to find a rare magical item that is said to have the power to save Galuna Island from a new threat. Another could be that the girl from Galuna has a special power that Natsu needs to unlock his own new level of magic. Maybe they start off as rivals, competing to be the best in a magical tournament but then gradually fall in love as they discover more about each other.
The OC could be a time - traveler who ends up in the Fairy Tail world. She meets Natsu and tries to hide her true identity. But Natsu, being perceptive, notices something odd. They start to team up for various missions, and the OC has to use her knowledge of future events to help Natsu and Fairy Tail, all the while falling for Natsu's brash but kind personality.
One idea could be that Natsu and Lisanna are partners for a big school project. They start off not getting along well because of their different work styles. Natsu is more impulsive and wants to get things done quickly without much planning, while Lisanna is very organized. But as they work together, they gradually discover each other's good qualities and start to fall for each other.
Well, one possible plot could be that Natsu is betrayed in his own world and somehow ends up in the DxD Highschool universe. Maybe he has to deal with the different power dynamics and politics there while also trying to figure out who betrayed him in his original world. He might form new alliances with the characters in DxD Highschool and use his unique abilities to survive and seek revenge for his betrayal.