A human male detective could be investigating strange occurrences in the city when he encounters a Kryptonian female superhero. They start working together to solve crimes and protect the city. Along the way, their relationship blossoms as they discover they have more in common than they thought, like their strong sense of justice.
A plot could involve a human male athlete who befriends a Kryptonian female. She has powers that she's still learning to control. He helps her train in a different way, focusing on her mental strength rather than just her physical powers. Their relationship grows as they train together, and they face competition from other superhumans who don't like their cross - species friendship.
Maybe the Kryptonian werewolf is a protector in a different way. Instead of being a traditional hero like Superman, the werewolf form gives them unique abilities to protect the city at night or in certain dangerous situations. They could form an unlikely alliance with other characters in Metropolis, like a detective who is trying to solve a series of crimes that seem to be related to the werewolf's presence.
Another interesting concept is a Kryptonian OC who is part of a secret society on Earth. They keep their identity hidden from the world, but within this society, they use their powers to maintain order and justice in a more shadowy way. They might have to deal with internal power struggles within the society as well as external threats to their secrecy.
In this fanfic, there could be a scenario where Batman is exposed to Kryptonian technology that gives him some Kryptonian - like abilities temporarily. A Kryptonian comes to Earth to study this anomaly. They start off as adversaries but as they learn more about each other, they find that they can work together to protect Earth from a greater threat that only their combined skills can defeat.
A possible fanfic plot could involve the female Charizard being a sort of guardian of an ancient and mysterious place. The male human stumbles upon this place and initially, the Charizard is hostile. But as time passes, they realize they have common goals in protecting the secrets of the place. Their relationship then develops into a deep friendship, with the human learning about the Charizard's world and the Charizard learning about human emotions.
It can be a relationship of mutual respect. The Kryptonian respects Batman's intelligence and determination despite being a mere human. Batman respects the Kryptonian's power and their sense of justice. They might have different approaches to solving problems, but they recognize the value in each other's methods. For instance, when facing a powerful villain, Batman would come up with a strategic plan while the Kryptonian uses their powers to execute it.
First, it should focus on how they interact in their natural habitats. For example, if the male human stumbles upon the female wolf in the forest, their initial reactions would be based on their instincts. The human might be cautious, while the wolf might be defensive. Then, through small acts of kindness like sharing food or protecting each other from common enemies, their relationship can start to develop.
The language barrier could be a challenge. Goku speaks his own language, and although he can communicate with others on Earth, the Kryptonian woman might have a completely different language. They would need to find a way to communicate effectively, perhaps with the help of some sort of translation device or learning each other's languages. Another challenge could be the expectations of their respective communities. Goku has his friends and family on Earth who might be wary of this new relationship, and the Kryptonian woman might have her own set of people (if there are any other Kryptonians left) who have different views on inter - species relationships.
You can develop their relationship through communication. Even though they may not speak the same language at first, they can find ways to understand each other. The male human could learn about Lucario's body language and the female Lucario could start to recognize the human's emotions. This mutual understanding will bring them closer. Also, they could have moments of vulnerability where they rely on each other for support, like when the Lucario is injured and the human protects her, or when the human is in trouble and the Lucario uses her powers to save him.
A possible plot could involve the male human being a trainer who has a unique connection with the female Lucario. They enter a Pokémon tournament where they face numerous challenges together, not only in battles but also in dealing with the politics and rivalries among other trainers. Their relationship deepens as they rely on each other to succeed.