In a more complex plot, Oberon falls in love with a character in the Harry Potter world. Harry becomes involved as he tries to help Oberon navigate the human - or rather wizard - emotions and social norms. This could involve dealing with other magical beings in the Potter universe who are suspicious of Oberon's presence and intentions.
Yes, there are some out there. You can start by looking on fanfiction websites like Archive of Our Own. Some authors might have explored this unique relationship in creative ways, perhaps imagining a crossover world where the two characters meet and form a bond. However, it's a rather unconventional pairing, so the number of such fictions might be limited compared to more common pairings in the Harry Potter fandom.
A plotline might involve a quest. Suppose there is a dark force threatening both the wizarding world and Oberon's realm. Harry and Oberon, being lovers, decide to embark on a journey together to stop this threat. Along the way, they face various challenges that test their relationship. They might also discover new magical abilities or secrets about each other's worlds that strengthen their bond.
One idea could be a crossover where the magic from the Harry Potter world is introduced to the vampires in Diabolik Lovers. For example, a Hogwarts student could accidentally end up in the Diabolik Lovers' world and use spells to both defend themselves from the vampires' advances and also try to find a way back home.
Oberon is also a main character. He is a powerful figure from fairy lore. In this fanfiction, he would be the one with his own set of powers and motives that interact with Harry Potter's world. He might bring his own brand of magic and chaos to the story.
Another great plot idea is the cultural exchange between the two universes. The proper British wizarding society in Harry Potter and the more gothic, dark world of Diabolik Lovers. How would the characters from each world react to the different social norms? For instance, how would the vampires react to the Hogwarts house system? And how would the wizards deal with the vampires' feeding habits? This can lead to a lot of humorous and also thought - provoking situations in the fanfiction. It can also explore themes like acceptance and prejudice as the two groups interact.
Oberon is likely a character from the fairy realm. In this fanfiction, he is Harry Potter's mate. He might be based on the traditional Oberon from fairy lore, a powerful and somewhat mischievous fairy king who now forms a special relationship with Harry.
One idea could be that Harry and Tom meet in an alternate universe where they are not enemies. They discover they have a shared love for magic theory and start to study together, gradually developing feelings for each other. Another plot could be that they are forced to work together on a dangerous mission. Through facing hardships side by side, they realize their connection.
In the 'Harry Potter and Oberon are mates fanfiction', the plot could be centered around the cultural and magical differences between wizards and fairies. Oberon, being Harry's mate, has to introduce Harry to the fairy society. Harry, in turn, has to deal with the prejudice from some fairies who don't trust wizards. Meanwhile, they both work together to solve a mystery that threatens both the wizarding world and the fairy realm, such as a dark force that is trying to break down the barriers between the two worlds.
The plot might revolve around a conflict where Harry's descent from Oberon makes him a target. Voldemort could want to use his unique heritage for his own dark purposes. Harry then has to navigate this new threat while also learning about his fae heritage, which includes things like learning new spells or magic related to Oberon's lineage.
A friendship - centered fanfiction would be cool. Maybe a new character befriends the vampires not out of fear but because they see the good in them. This character could slowly break down the walls the vampires have built around themselves and change their relationships with each other.