The main themes can vary widely. But often there is the theme of adaptation. Since she is in the High School DxD world, she has to adapt to different situations. Love is also a theme sometimes, whether it's romantic love or love for her comrades. And there's the theme of destiny, like what her true purpose is in this fictional universe which is full of magic, power struggles and various factions.
I've come across 'Lady Phenex's Redemption'. This fanfiction is about her journey to redeem herself for past actions. The story is engaging as it shows her growth and transformation. There's also 'Lady Phenex and the Forbidden Magic' which is filled with mystery and adventure as she gets involved with some powerful and forbidden magic in the High School DxD world.
One great 'oc phenex dxd fanfiction' is 'The Phenex's Ascent'. It has a really engaging plot where the OC Phenex character has to face various challenges in the DxD universe and overcomes them with unique powers and clever strategies.
One common theme is power - up. Since Naruto is already a powerful character in his own right, and the DxD world has its own power system, often in these fanfictions Naruto gets new powers or finds ways to combine his existing powers with DxD elements. For example, his chakra could be combined with the magic in DxD.
One interesting 'Naruto Phenex DxD Fanfiction' could be 'Naruto in the DxD World'. It combines the elements of Naruto's skills and the unique world of DxD quite well. The story often has Naruto using his ninja abilities in the DxD universe, which makes for some exciting battles and interactions with the DxD characters.
The popularity of 'oc phenex dxd fanfiction' might be due to the fact that it allows for a lot of creativity. People can create their own unique characters within the established DxD universe, like the Phenex. It gives fans a chance to explore different storylines that the original might not have covered.
One common theme is power growth. Since Ravel is from the Phenex family, many fanfictions explore her developing her powers and how she uses them. Another theme is friendship. Ravel often forms new friendships or strengthens existing ones in these stories.
Maybe the plot involves Naruto being sent to the dimension where Lady Phenex lives for some unknown reason. Lady Phenex is a very important figure in her world, and Naruto's sudden appearance causes a stir. At first, there's a lot of misunderstanding and Naruto has to prove that he means no harm. Eventually, they discover that there are some similarities between their powers, and they train together to become stronger. This new - found strength then helps them to save both of their dimensions from a great catastrophe.
His complex personality. Riser is initially portrayed as a bit of a villain, but he has his own motives and insecurities. Fanfiction writers like to explore these aspects, like his pride which is both his strength and his weakness.
There might be a fanfiction where Riser Phenex discovers a new power within himself. This could lead to a whole new set of adventures as he tries to master it and also deal with the political implications within the Highschool DxD universe, like how other devil families react to his newfound strength.