One challenge is getting the power systems right. Naruto has chakra - based powers like ninjutsu and DxD has magic and devil powers. Combining them in a believable way can be difficult.
One common theme is the clash and combination of different power systems. Naruto has his chakra - based ninja powers, while the DxD universe has its own system of magic and power levels. So, seeing how these interact is a big part of it. For example, Naruto might teach Sona some ninja techniques.
One common theme is the power struggle. Since both Naruto and DxD have complex power systems, in the fanfiction, Naruto often has to prove himself in the DxD world which has its own set of powerful beings. Another theme is friendship. Naruto is known for his ability to make friends, and in these crossovers, he forms new friendships in the DxD world.
One good Naruto x Akeno DxD fanfic could be 'Naruto: The Shinobi in the DxD World'. It often has an interesting plot where Naruto's ninja skills blend with the supernatural elements of the DxD universe. The character interactions, especially between Naruto and Akeno, are well - written and add depth to the story.
Well, in a 'Naruto x Greyfia Highschool DxD' fanfiction, perhaps Naruto is a new transfer student in the Highschool DxD. Greyfia could be a popular student there. Naruto's positive and energetic attitude might attract Greyfia's attention. They could start off as friends and gradually develop a deeper relationship. Maybe they get involved in the supernatural battles of the DxD world together, with Naruto using his Rasengan and other jutsu while Greyfia uses her demonic powers. And as they spend more time together, they learn from each other's worlds and values.
One possible plot could be that Naruto is somehow transported to the Highschool DxD universe and meets Gabriel. They might team up to face a common threat that is endangering both the ninja world and the supernatural world of Highschool DxD. Naruto's unique skills as a ninja could be combined with Gabriel's angelic powers in an epic battle against evil forces.
Maybe Venelana has some connection to a powerful artifact in the Naruto world. Naruto and Venelana then have to embark on a journey to find this artifact before it falls into the wrong hands. Along the way, they learn about each other's cultures and powers.
Power - up themes are also common. Naruto already has his powerful ninja abilities, and when combined with the magic and power systems in High School DxD, there are often scenarios where he or Sona gain new powers or find new ways to use their existing ones. For example, Naruto might learn to combine his chakra with Sona's magic for a super - attack. Another theme is friendship and alliance. Since they are from different worlds, they need to form an alliance to face common enemies. This often leads to the development of a deep friendship between them as they rely on each other's strengths.
One possible plot could be that Naruto somehow gets transported to the DxD universe and meets Yasaka. They initially have a misunderstanding as Naruto's chakra and power seem strange to the beings in DxD. But as they get to know each other, they team up to face a common enemy that threatens both the ninja world Naruto comes from and the DxD world. They combine their unique abilities, Naruto's Rasengan with Yasaka's fox - like powers, to defeat the enemy and in the process, they become good friends and learn a great deal about each other's worlds.
One possible plot could be that Naruto, with his godlike powers, ends up in the world of Highschool DxD. He might join the Occult Research Club and use his unique abilities to protect the club from various threats. His ninja skills and super - powered jutsus could be a huge asset in battles against devils, fallen angels, and other supernatural foes.