One common theme is redemption. Maybe Odin is trying to make up for past wrongs towards Loki. Another is family drama, as their relationship is complex in the original mythology.
Yes, there are quite a few. You can start by looking on popular fanfiction websites like Archive of Our Own. There, you'll find various takes on the 'odin loves loki' concept. Some might explore it in a more platonic way, while others could be more on the romantic side.
A theme of acceptance is also prevalent. Loki is often seen as an outcast, and Odin's love can represent acceptance of Loki's true self, whether it's his magical abilities, his different nature compared to the other Asgardians, or his past mistakes. This acceptance can be a slow and arduous process in the fics, full of emotional ups and downs.
One great 'odin loves loki fanfic' is 'A Father's Unspoken Love' on FanFiction.net. It delves deep into Odin's complex feelings for Loki, exploring their relationship from a more emotional and psychological perspective.
Another theme is destiny. Fans often write about how Naruto's pre - determined path as a hero in his world might be affected or enhanced by Odin's presence. It could be that Odin has some foreknowledge that he imparts to Naruto, changing his course of action.
Well, it could be that Naruto somehow gets transported to the world where Odin exists and is mistaken for a powerful being like Odin. Maybe he has to take on Odin - like responsibilities and use his Naruto - skills in a new and strange setting.
A common theme is the clash of different power systems. Since Odin comes from Norse mythology and DxD has its own complex power structure, seeing how they interact is often explored. Another theme is the idea of prophecy. How Odin's knowledge of the future might play a role in the DxD world's events.