Read manga: Sayonara, Papa.

manga
Summary:

In kindergarten, naive Mitsuko began to think of Yoshioto, who was staying at her house, as her papa. And she vowed that she would be Yoshioto's bride when she grew up. Can this dream be fulfilled? In the journey to see him, she slowly understands her own feelings and her heart that refuses to mature, but nonetheless thinks she's already mature. In her search, they gradually melt into one.