They could be best friends. Tony might be the first human to accept Rudolph for who he is, and Rudolph might see Tony as someone he can trust completely.
Friendship is a very common theme. Since Tony and Rudolph are the main characters in this fanfiction concept, their bond and how they support each other through different situations is often explored.
Rudolph is often cautious and thoughtful, while Tony is more impulsive and bold. Tony's boldness can encourage Rudolph to take risks he might not otherwise take, and Rudolph's caution can keep Tony from getting into too much trouble.
One place to start looking for such fanfiction could be popular fanfiction websites like Archive of Our Own. Just search for 'the little vampire tony x rudolph' on there, and you're likely to find some interesting reads.
Well, it could be about Rudolph and Tony going on an adventure together. Maybe they explore a spooky old castle that has some hidden secrets. They might encounter other supernatural beings and have to work together to overcome challenges.
They could go on a journey to find a hidden vampire lair. Maybe they'd encounter other mythical creatures along the way and have to use their wits to outsmart them.
There could also be a character like a wise old vampire in the community who acts as a mentor to Rudolph, guiding him through the difficulties of being a young vampire in a world that has both vampire and human elements.
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 good tony x rudolph fanfiction could be about their adventures in a magical forest. They might discover hidden treasures and face challenges together, strengthening their bond along the way.
Another option is FanFiction.net. It's one of the oldest and largest fanfiction platforms. Just use the search function and type in 'tony x rudolph' to see if there are any relevant stories.