Love is also a prevalent theme. It could be Finn's love for a particular character, or the love others have for him. Sometimes it's a forbidden love which adds an interesting twist to the story. Additionally, the theme of redemption can be found in some fanfictions. Finn may have done some bad things in his past as a vampire king, and the story could be about his journey towards redemption.
One great finn the vampire king fanfiction is 'Finn's Reign' which delves into his early days as a vampire king. It has an interesting plot that shows his struggles to maintain power while dealing with internal vampire politics.
Well, 'Kicking Blood A Vampire Love Story' could be centered around the idea of a vampire couple. The 'kicking blood' part might be a really interesting concept. It could be that they are breaking free from the traditional ways of vampires, like the blood - sucking and all that, and their love is something that makes them do so. For example, one vampire might be in love with a human and they find a way to exist without harming others for blood, which is like 'kicking' the old vampire ways. It could also be some sort of vampire power or ritual related to their love that we don't know yet.
In many fanfictions, Finn's relationship with other characters gets explored in depth. For example, his interactions with his siblings could be different from the original series. He could be a more central figure in a story about the origins of the vampires in a fan - created lore.
One possible scenario could be that Finn, after being turned into a vampire, struggles with his new identity. He might have to deal with the urge to drink blood while still holding onto his old values. For example, he could try to find alternative ways to satisfy his thirst that don't involve harming humans, like drinking animal blood.
One common theme is the struggle between Finn's vampire nature and his human side. For example, in many stories, he has to resist the urge to feed on humans while also trying to fit into a human society.
Finn's role in fanfiction can be a supporting character that adds depth to the main plot. He might be used to introduce new elements to the vampire mythology.
One possible scenario in this fanfiction could be that Finn's transformation into a vampire brings out a whole new side of his personality. He might struggle with his newfound thirst for blood while still trying to uphold his heroic values. Maybe he teams up with Marceline, who is already a vampire, and she teaches him how to control his urges.
Finn's personality would probably become more brooding. The whole vampire thing is a big change, and he might start to withdraw a bit. He was always so full of energy and positive before, but now he could be more cautious and a bit more on the dark side. He might also become more territorial, like vampires tend to be.