If you're looking for manga similar to Gunjou Gakusha, you might like these titles.
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.
A young girl whose sick-seeming friend insists that she be taken to the ocean. Without asking any questions, she enlists the help of a random passing driver to fulfill her friend's strange wish. The reason for it will end up being stranger than she could have guessed! Another story involves a young girl whose older sister has an illness that has left her asleep for 8 years. One day, her older sister wakes up, and the two share their first real day together.