One idea could be to write about the little vampire's first day at a human school. He has to hide his fangs and his love for blood while making friends. It would be full of comical situations like when the cafeteria serves steak and he has to resist the urge to pounce on it.
Another idea is to explore a story where the little vampire gets lost in the human world during a full moon. He has to find his way back home while avoiding hunters and also dealing with the strange things humans do at night. This could show his vulnerability and his growing understanding of the human world.
One idea could be a crossover with a popular wizarding world. The little vampire could attend a magic school and have adventures with the wizard students, facing magical creatures together. Another idea is to cross it over with a time - traveling story. The vampire travels through different eras, experiencing different cultures and historical events.
One idea could be exploring the vampire's family history more in - depth. Maybe there are ancient secrets or rivalries within the vampire clan that the main characters could uncover.
Perhaps Rudolph discovers a hidden power within himself that helps him protect his vampire family from a new threat in their town. This could involve a series of challenges where he has to learn to control this power.
Perhaps the fanfiction could explore a friendship between the little vampire and a human who discovers his secret. They could go on adventures together, with the human helping the vampire understand human emotions better, and the vampire using his powers to protect the human from danger.
One idea could be the little vampire befriending a human who is also a slasher movie fan. They bond over their differences and similarities, like the vampire's nocturnal nature and the human's love for horror. The vampire could show the human the 'vampire version' of horror, which is their everyday life.
A really interesting plot could be that Gregory gets lost in the human world during the day. He has to find his way back home while avoiding being discovered by too many humans. He could meet a kind old lady who helps him without really knowing what he is, and through this encounter, he learns more about human kindness.
Maybe the OC has a special power or ability that Rudolph needs. For example, the OC can sense when danger is near. They team up to protect Rudolph's vampire family from a group of hunters who have come to town. As they work together, a deeper bond forms between them.
One idea could be a vampire who is drawn to the lead singer of a rock band in 'Gravitation' due to the passion in their music, which is like a siren call for the vampire. Another could be a vampire that uses their powers to help the 'Gravitation' characters achieve their dreams in the music industry in exchange for small amounts of blood. Maybe a vampire who was once a famous musician in the past and now finds a connection with the modern music scene in 'Gravitation' and falls in love with one of the characters.
A fanfiction could focus on the backstory of a minor vampire character in Vampire in the Garden. For example, how they were turned and their struggles to adapt to the vampire lifestyle while still having some remnants of their human emotions.
One idea could be Ranma turning into a vampire instead of a girl when splashed with cold water. It would add a whole new twist to his already chaotic life. He could struggle with his new vampire instincts while still dealing with his fiancées and martial arts rivals.