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 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.
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.
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.
Another common pairing is Sasuke and Akeno. Sasuke's brooding and powerful nature might attract Akeno, who is also quite powerful and has a bit of a mysterious side herself. They could bond over their shared power levels and a mutual understanding of what it means to be different from the norm in their respective worlds.
Harry Phenex himself is often a very popular character. Since he is the main focus in this fanfiction concept, his unique background as a Phenex in the Highschool DxD setting makes him stand out.