Yes, there are some out there. You can start by checking fanfiction websites like Archive of Our Own or FanFiction.net. Just search for 'naruto x yasaka' on their platforms and you might find some interesting stories written by fans.
One common theme is adventure. Since both Naruto and Yasaka are from different and interesting worlds, fanfictions often send them on exciting adventures. Another could be friendship, as they get to know each other.
There could be. Fanfic writers often come up with various pairings, and 'naruto x yasaka' is not an uncommon type of crossover idea. However, it may not be as mainstream as some other pairings in the Naruto fandom. To find it, you might also want to check Naruto - specific fanfic communities where fans share and discuss their works.
In fanfiction, Naruto could be portrayed in various ways. He might be a character with new relationships and roles. Without reading the specific 'naruto father of yasaka fanfiction', it's hard to say exactly. But generally, he could be a father figure to Yasaka, which would likely involve a lot of character development and new storylines related to protecting, guiding, or having a special bond with Yasaka.
One possible plot could be Naruto being somehow transported to the world of Highschool DxD. He could use his ninja skills and chakra in the battles against the devils and fallen angels in that world. Maybe he teams up with Issei and his group, and Naruto's unique jutsus like Rasengan and Shadow Clone Jutsu surprise everyone.
One possible fanfiction could involve a crossover where the characters from Highschool DxD and Naruto meet in a unique world. Yasaka, being a powerful figure in the Highschool DxD universe, might interact with Naruto characters. For example, she could form an alliance with Naruto to fight against a common enemy that somehow threatens both of their worlds. Maybe a group of rogue ninjas from Naruto's world team up with some rogue devils from Highschool DxD.
One popular 'Naruto and Yasaka married' fanfiction might be 'Naruto: The Kitsune's Husband'. It explores their relationship in a world where Naruto somehow ends up in the Youkai realm and marries Yasaka. The story has some interesting twists on Naruto's powers and how he adapts to the new culture.
A common theme is power. Since both Naruto and Yasaka are powerful in their own rights, many fanfictions explore how their powers interact and combine. Another theme is friendship. They often form a strong bond in these stories.
Lemon could be a magical fruit in the fanfiction that gives special abilities to those who consume it. Naruto, Kuroka, and Yasaka could be on a quest to find more of these Lemons to gain power for their respective goals.
One challenge could be cultural differences. Naruto is from the ninja world with its own set of values and traditions, while Yasaka is from the youkai world. Another might be the acceptance of their relationship by their respective communities. The ninja might be suspicious of a youkai, and the youkai might not fully trust a human like Naruto at first.