One common theme is the 'fish out of water' scenario. Hermione, coming from the wizarding world of Harry Potter, is in a very different setting with Thranduil from Middle - earth. Another theme is the exploration of their different magical abilities and how they interact. For example, Hermione's knowledge of spells and Thranduil's elven magic.
You can start by looking on fanfiction.net. It has a large collection of fanfictions across various fandoms, and there's likely to be some great Hermione and Thranduil ones there. Another option is Archive of Our Own (AO3). It has a very active community and a wide range of fan-created works, often with detailed tagging systems that can help you find exactly what you're looking for.
Thranduil can be developed by showing his vulnerability. With the OC being pregnant, he might worry about losing her or the unborn child. This could make him more relatable. For example, he might show a side of himself that is less regal and more human - like in his concerns. Another way is through his interactions with the OC. He could be more affectionate, like gently touching her belly and sharing his hopes for the future with her.
There's also 'The Elven Heart'. This story focuses on a time when Tauriel is injured and Thranduil must care for her. It explores their feelings for each other that they have long kept hidden. The dialogue is well - written and gives a lot of insight into their characters.
In RWBY fanfiction, King Thranduil can be a really interesting addition. He could bring his elven grace and combat skills. For example, he might form an alliance with the RWBY characters. His leadership and wisdom could be a great asset in the fight against the Grimm. Also, his unique appearance would surely stand out in the RWBY universe.
King Thranduil can play the role of a powerful ally. He has his own army and resources which could be useful for the RWBY characters. For instance, his archers could help in battles against the Grimm.
Most Thranduil love fanfiction involves beautiful descriptions of the elven realm. It's like the love story is set against this backdrop of a magical, forest - filled world. The love is also often depicted as something that is both forbidden and irresistible, adding an element of drama.
One great Thranduil fanfiction is 'The King's Redemption'. It delves into Thranduil's past and his inner struggles. Another is 'Thranduil's Quest', which takes him on an adventure outside of Mirkwood. And 'A Day in the Life of Thranduil' gives a really interesting peek into his daily routine in the elven kingdom.
The allure lies in the contrast between them. Fem Bilbo can be depicted as a character with a kind heart and a curious nature, while Thranduil is a majestic and often mysterious elf - king. In fanfiction, their paths might cross during a quest. Their initial misunderstandings could lead to a great story arc, where they gradually learn about each other and overcome their differences.
Thranduil and Legolas' mother is another pairing that appears in some fanfictions. Since not much is known about Legolas' mother in the official lore, it gives fanfic writers a lot of room to create their own stories about Thranduil's relationship with her, often adding a touch of mystery and historical depth to the romance.