This feels like a match made in a very specific corner of fanfiction.net, and honestly? The blend works better on paper than you'd think. Naruto's core is built on a hidden world of ninja magic existing alongside a normal society, while 'High School DxD' basically does the same thing with devils, angels, and fallen angels.
You slap Naruto into Kuoh Academy, and the action mechanics slot right in. He's already a walking supernatural arsenal – shadow clones become a perfect foil for a devil's peerage, the Rasengan could be a new type of sacred gear, and the whole jinchuriki thing? That's just a different flavor of possessed hero. The high school setting gives a familiar social structure for the power scaling; instead of chuunin exams, you have rating games.
Where it gets messy is tone. Naruto's action has a shonen sincerity, a lot of talk-no-jutsu and hard-won camaraderie. DxD leans heavily into ecchi comedy and harem politics. A crossover either has to sand off Naruto's edges to fit into the more... relaxed atmosphere of DxD's school life, or it cranks up the stakes of DxD's world to match the existential threats Naruto's used to. I've read fics that go both ways, and the ones that work best pick a lane. Trying to be 100% both usually ends up a tonal car crash.
Honestly, the most interesting fusion isn't the big flashy fights, it's the mundane stuff. Imagine Naruto trying to explain chakra theory to a baffled Rias Gremory, or Issei completely failing to understand why Naruto isn't trying to peek into the girls' bathhouse. That cultural clash is the real gold.