In a more romantic - themed fanfiction (while still keeping it appropriate), Naruto could find himself attracted to both Rias and Akeno in different ways. His kind heart and strong will might draw them to him as well. However, he has to navigate the cultural differences between their worlds and his own. There could be a lot of misunderstandings at first, but as they spend more time together, they start to understand each other better and form a deep bond that goes beyond just attraction.
A simple idea for a fanfiction could be a tournament - style story where Naruto, Rias, and Akeno all participate. Each would bring their own unique skills to the table. Naruto has his ninja abilities, Rias her devil powers, and Akeno her electrical attacks. It would be interesting to see how they compete against each other and then eventually team up against a common foe.