Hinata doesn't really know that much about sex and is helpless when puberty hits.
She had heard whispers about it, small comments in the girls' locker room, She goes to the library one day to settle her mind about what sex entails and is slightly disapointed when the only books available on the subject are either medical ones or Icha Icha novels. She picks a medical one and reads into it. It's graphic and raw but not erotic and she leaves the library thinking of sex as just another jutsu she can't master.
Her breasts double in the summer. She can't fit into her clothes and her body is out of proportion, since her height and waist haven't caught up with the sudden bust. Hair starts to grow in funny places and she understands just how lucky she is for having a female sensei when her period arrives during a mission.
All changes, all confusing and somewhat thought inducing. But that's not what troubles her the most.
Before, when Hinata thought about Naruto, it was with a mix of platonic love and adoration, something pure and almost spiritual. Her heart started beating faster, but that was about it. She remembered his smile and his energy. And she loved him in a childish way.
Now, though...something tingles, down there. She begins to feel an urge, but she can't tell what she urges for. It's a kind of thrist, but she's innocent and doesn't know how to get rid of it yet.
So she goes back to the library, but this time picks up an Icha Icha novel. It's too much for her, but one word of the two full pages she read lingers on – masturbation.
It all starts one night, when she is lying in bed and she thinks of how Naruto might look now. She changed a lot in just one summer, and he's been gone for two years now. She admires the change in her comrades and friends.
She imagines Naruto now. First his face...then his body. Then his hands. Then his hands touching her face. Then their faces meeting for a kiss.
The fantasy evolves and feels that tingle again. She decides to try out that thing in the Icha Icha novels. At first, she's clumsy, but when the pleasure is first felt, she realises she's a natural.
She experiences her first orgasm in her bed, with Naruto in her head. She starts doing it every night, and she begins to feel more like a woman. So she lets her hair grow and is proud to be growing tall and curvy. She's a beauty by the time Naruto comes back.
But she can't stand speaking to him. She admires his looks for afar and is curious to be closer. However, her heart nearly stops when he greets her inches away from her face.
When she finally feels free to look at him closely, she realises the real thing will always top the fantasy.
And from that point on, the orgasms roll in each night, each one more powerful than the last, preparing for the time she will no longer have to satisfy herself.