Perhaps in this fanfiction, Leah has a special power that Naruto needs to learn in order to defeat a new and powerful foe. Naruto starts training with Leah. Along the way, they learn about each other's pasts, their dreams and fears. As Naruto masters the power, they also form a bond that is unbreakable. And this bond could be the start of a new relationship, whether it's a romantic one or a very strong friendship.
One possible plot is that Leah is from a different village and she comes to Konoha. Naruto is assigned to show her around. At first, Naruto is his usual boisterous self and Leah finds it annoying. But then they discover a common enemy that is threatening both their villages. They then combine their unique skills, Naruto's Rasengan and Leah's special elemental magic (assuming she has some in this fanfic), to defeat the enemy and in the process, fall in love.