You should also consider the theme of your fanfiction. Are you aiming for an action - packed adventure, a heartwarming friendship story, or a romantic tale? Once you've decided on that, start building the plot. Outline the main events, the challenges they'll face, and how their relationship will develop. For example, if it's an adventure, think about the villains they'll fight and how they'll use their skills together.
Another important aspect is the writing style. Try to mimic the tone of the Naruto series. Use vivid descriptions for the battles and the emotions of the characters. Also, don't be afraid to add your own unique twists. Maybe give Oola a new power or create a new type of ninja art that Naruto has to learn from her. And always remember to proofread your work to make sure it flows well and is free of grammar errors.