Perhaps the female Grimm has a special power that is different from the other Grimm. Jaune discovers this and tries to use it to his advantage in a battle. But as they interact more, they develop a bond. The plot could involve them facing challenges together, like other more powerful Grimm who see their relationship as a threat.
The fanfic could start with Jaune getting lost in Grimm territory. There, he meets the female Grimm. At first, they are enemies, but then they realize they both have a common enemy. They have to work together to defeat this greater threat, and during this process, they gradually change their views of each other and develop a deep relationship.
One idea could be that the female Grimm is an outcast among her kind. Jaune, with his sense of justice, tries to understand her instead of immediately fighting. They form an unlikely alliance and learn from each other, with Jaune teaching her about the value of life and she showing him the secrets of the Grimm world in return.
Some niche fanfic communities or forums dedicated to the relevant fandom might also be a good source. For example, if there are specific Reddit communities for the series that features Jaune, you could ask around there if anyone knows of such a fanfic.
Sure. One common type of Jaune and female Grimm fanfiction involves Jaune being thrust into a situation where he has to team up with a female Grimm against a greater threat. This forces them to work together and understand each other's strengths and weaknesses. These stories often have a lot of character development for both Jaune and the female Grimm character.
One possible plot could be that they start off as rivals in Beacon Academy. Cardin is his usual bully self at first, but as he gets to know 'female Jaune Arc', he starts to see her in a different light. They could be paired together for a mission and through that, they learn to trust and rely on each other, slowly developing feelings.
One idea could be that Jaune Arc discovers a lost dragon egg. When it hatches, a female dragon emerges. The dragon has unique powers that Jaune has to help her control. They form a bond as they face various threats in the world together.
Well, perhaps the plot could involve Jaune trying to train the pet Grimm. He might face challenges from other characters who are against having a Grimm as a pet due to their inherently dangerous nature.
One idea could be Harry discovers a hidden power within the Grimm world that no one else has. This new power could lead him on a journey to uncover secrets about the origin of the Grimm. Another idea is Harry befriends an outcast Grimm creature and together they face the prejudices of the Grimm society.
You can try some popular fanfiction websites like Archive of Our Own. It has a large collection of fanfictions from various fandoms, and there's a good chance you'll find Jaune and female Grimm fanfictions there.
One idea could be a story where Velvet discovers a new type of Grimm with unique abilities. She then has to figure out how to combat it, using her skills and the help of her friends. Maybe she could study the Grimm's behavior and weaknesses in secret to surprise everyone when she reveals her knowledge.
One plot idea could be a group of hunters discovers a new type of Demonic Grimm that can possess other Grimm, creating an army. They have to find the source of this new threat and stop it before it overcomes all of Remnant. Another could be a young huntress in training who has a special ability to sense Demonic Grimm and she teams up with some unlikely allies to face a powerful Demonic Grimm lord that has been hidden for centuries. A third idea is that the Demonic Grimm start to corrupt the minds of some of the hunters, turning them against their own kind, and the remaining hunters have to fight both the Demonic Grimm and their former comrades.
One idea could be Ruby facing a new type of Grimm that has unique abilities, like the ability to manipulate time in a small area. This would put Ruby in a tough situation where she has to figure out how to combat it while being affected by the time distortion. Another plot could involve Ruby getting lost in a Grimm - infested area and having to rely on her wits and the little resources she has to survive and find her way back to her team.