Definitely! High School DxD has a manga. It brings the world and adventures of the series to life in a different medium, giving fans another way to engage with the content.
As of now, there doesn't seem to be any news of new High School DxD manga being produced. Usually, such information would be shared through official channels or fan communities, but nothing has come up yet.
In a Naruto and High School DxD fanfiction, there could be a scenario where the protagonists of both stories meet in a neutral dimension. Issei from High School DxD might be intrigued by Naruto's ninja skills and determination. Naruto, in turn, could be curious about Issei's Sacred Gear. They could start training together, sharing their knowledge and skills, and ultimately have to face a common enemy that threatens both their worlds.