Well, it could be that there's a new villain in the Power Rangers' world who has the ability to create chaos by causing people to act out of character. This affects the Loud family back in their world too. So, a group of Power Rangers come to the Loud House world to stop it. The Loud kids then team up with the Rangers. For example, Luna and Luan could use their musical and comedic talents respectively to help the Rangers in their fight. They could create a distraction with a funny skit while the Rangers set up their final attack on the villain.
Maybe the Power Rangers' technology gets scattered across different dimensions, and some of it lands in the Loud House world. The Loud kids start to mess around with it and accidentally activate a signal that attracts the attention of both the Power Rangers and their enemies. The Rangers then come to retrieve their tech. But they find that the Loud family has some unique skills and qualities that can actually help them in their fight against a new, powerful enemy. So they form an alliance, with each Loud kid contributing in their own special way, like Lynn using her athleticism in combat and Lucy using her spooky knowledge to deal with some of the more supernatural aspects of the enemy's powers.
I think Lincoln would be the most likely. He's the main character among the Loud kids and often takes on leadership roles in his own family situations. He's also curious and adaptable, which are good traits for a Power Ranger. He would be eager to learn about the Ranger powers and use them to protect both his family and the new world he's a part of.
One possible plot could be a crossover where the Bakugan and Power Rangers have to team up to fight a common enemy. Maybe an ancient evil has the ability to disrupt both the Bakugan battles and the Power Rangers' world, so they combine their unique powers and skills to defeat it.
One possible interesting plot could be that the Naruto characters somehow end up in the Power Rangers' world. Maybe Naruto and his friends are mistaken for new recruits by Zordon. They then have to learn how to use the Power Rangers' technology while also teaching the Rangers some of their ninja skills, like chakra control and stealth. Together, they face a new enemy that is a combination of Naruto's villains, like Orochimaru, and the Power Rangers' classic foes, creating a unique and challenging battle scenario.
Another possibility is that it's a story of unrequited love at first. Lincoln might have feelings for Becky, but she's initially unaware or has her own concerns. The fanfic could then show how he tries to win her over, through acts of kindness, shared interests, and by being there for her during tough times.
A plot might involve a ghoul ending up in the Loud House world. This ghoul could be on the run from other ghouls or the CCG in its own world. In the Loud House, it has to hide its true nature from the Loud family while also trying to adapt. The Loud kids start to notice strange things happening around the house, like missing food (because the ghoul needs to eat). Eventually, they discover the truth and have to decide whether to help the ghoul or turn it in.
One possible plot could be that the OC is a new ranger from a different dimension. Jayden meets her during a battle against a powerful new enemy. At first, they have some misunderstandings due to their different fighting styles and backgrounds. But as they fight side by side more often, they start to understand and respect each other. Eventually, they develop feelings for one another while protecting the world from the growing evil forces.
Maybe Linkin is from a different dimension and he accidentally lands in the Loud House world. He and Lily form a unique bond as he tries to find his way back home. They go on adventures together in the neighborhood, with Lily showing Linkin all the local quirks and Linkin teaching her some of his world's secrets.
Well, perhaps the ghouls from Ghoul School are on a field trip to the human world and end up in Royal Woods. They meet the Loud family and chaos ensues at first as the Loud kids are scared. But then they realize the ghouls are friendly. Together, they have to figure out how to get the ghouls back to their school before the sun rises, which is dangerous for the ghouls. And along the way, they learn about each other's cultures and make new friends.
Another possibility is that there's a crossover of characters' identities. A Power Ranger could gain Beetleborg powers and vice versa. This would lead to some interesting character development as they learn to control new powers and deal with the changes in their fighting styles and relationships with their respective teams.
In a Power Rangers fanfic with bunny love, perhaps the bunny is a magical creature that was once a Power Ranger but was cursed into a bunny form. The other Rangers don't initially recognize it. As the story unfolds, the bunny - Ranger tries to communicate with them through its actions. And during this process, a love story could develop between the bunny - Ranger and one of the current Rangers, adding an interesting twist to the typical Power Rangers narrative.