One great fanfiction could be 'Asmodeus' Unlikely Mate'. It delves into an interesting relationship where the main character, against all odds, becomes Asmodeus' mate. The story is filled with action and some unique interpretations of the Supernatural lore.
Love against all odds is a big theme. Despite Asmodeus being a feared demon, the fanfictions often show his mate falling in love with him regardless. There's also the exploration of identity. The mate may question their own identity as they become part of Asmodeus' world. Additionally, loyalty is a theme that is explored. The mate has to decide whether to be loyal to Asmodeus, to their own kind, or to some other moral or ethical code.
I really like 'The Mate of Michael in the Supernatural World'. This fanfic does a wonderful job of exploring the relationship between Michael and his mate. It has some really intense emotional moments and also some exciting action scenes that are typical of the Supernatural universe.
There's 'A Mate for the Archangels'. This fanfiction is quite detailed in its exploration of Michael and Lucifer as mates. It not only focuses on their relationship but also how it impacts the other characters in the Supernatural universe. It has a slow - burn aspect to it which makes the development of their relationship feel more natural and believable.
Well, I've read a story where a supernatural female, who has the power to control time, becomes Hades' mate. It was fascinating how the author explored their relationship against the backdrop of the Underworld. You might find it by searching for 'Time - Bending Female and Hades' in the relevant fanfiction archives. Usually, fanfiction sites like Archive of Our Own also have a good collection of such stories.
First, know the character well. Study how Asmodeus was portrayed in Supernatural - his mannerisms, his goals, and his relationships. Then, come up with a unique plot. It could be something that was only hinted at in the show or a completely new scenario. For example, you could write about his time before he became a major character in the series.
Another theme is redemption. Some fanfictions might depict Asmodeus in a journey of trying to redeem himself, despite his evil deeds in the show. This could involve him forming unlikely alliances or having a change of heart due to certain events or characters. It's interesting to see how authors play with his character in this way. Well, and relationships are also a big theme. Whether it's his relationship with other demons, angels, or the Winchester brothers, exploring these connections can add depth to the story and show different sides of Asmodeus.
You can try fanfiction websites like Archive of Our Own (AO3). There are a large number of Supernatural fanfictions about Asmodeus on it. Just use the search function and type in 'Supernatural Asmodeus' to get relevant works.
Many Asmodeus fanfictions play with his powers. They might show him using his abilities in new and unexpected ways. For instance, instead of just the typical demon powers we see in the show, he could have some hidden powers that are only explored in the fanfiction. These can make for very engaging reads as they expand on the character in ways the original show didn't.
I really liked 'The Moonlit Mate'. In this fanfiction, the OC is a powerful healer who catches Sesshomaru's attention. The story is filled with adventure as they face various challenges together. It also delves deep into Sesshomaru's character, showing how he gradually opens up to the OC. And there's 'Destined Encounter' where the OC has a mysterious past which ties in with Sesshomaru's own journey. The writing is engaging and the relationship between the two characters feels very natural.
I really like 'Sirius and Hermione: A New Chapter'. In this fanfic, their relationship starts off rocky as they have to overcome their initial differences. Hermione is seen as the one who can help Sirius heal from his past traumas. The story is filled with a lot of emotional moments and some really well - written dialogue that makes you feel as if you're right there in the wizarding world with them.