One possible theme could be friendship. As they interact, they could form a deep bond that overcomes various challenges.
One common theme is adventure. Given their roles in the Okami world, many fanfictions send them on exciting quests.
In a 'amaterasu x waka fanfiction', the author might play around with the cultural backgrounds of these characters. Amaterasu is often associated with Japanese mythology. So the story could draw on that rich mythology while also developing Waka's character in a way that fits into this world. Maybe it shows how Waka respects and learns from Amaterasu's divine nature, and in turn, Amaterasu discovers something new about the mortal world through Waka.
One interesting fanfiction could be where Amaterasu and Waka go on a journey to discover a hidden part of their world. In this story, they might face challenges that test their bond and individual powers.
One common theme could be the exploration of their relationship in different mythological settings. Maybe how they interact with other deities in their world.
One common theme could be the clash or harmony of different powers. Since Issei might have his own set of powers and Amaterasu is a significant figure in mythology with her own powers, their interaction in terms of power dynamics can be a theme. For example, how they combine their powers to face a common enemy.
One common theme is the power dynamic. Naruto has his ninja powers, and Amaterasu has her divine abilities. How they interact with each other in terms of power, whether it's complementing or conflicting, is often explored. For example, they might combine their powers to defeat a powerful foe.
One common theme is the exploration of their opposing natures. Amaterasu is often seen as a symbol of good and light, while Oki represents more of a wild and somewhat darker force. Fanfictions might play with how they interact and balance each other out.
It could be a rogue ninja who has also discovered a way to harness the power of Amaterasu in a corrupt way. This ninja might want to use the power to take over the ninja villages and Naruto stands in his way.
Perhaps a powerful demon that has a grudge against the power of Amaterasu. It targets Naruto because he is the one who seems to be getting closer to Amaterasu. The demon could be from an ancient time when Amaterasu was first used to seal it away, and now it's back to stop Naruto from fully understanding and using Amaterasu.
One common theme is the exploration of their powers. Percy has his demigod abilities and Amaterasu has her divine powers, so stories often show how these powers work together or clash. Another theme is friendship or partnership, as they come from different mythologies but can form an alliance.