Kuchibiru ni Uta wo: 15-nengo no Kimi e

In an island with a Christian influence, is where a high schooler Nazuna lives. She had hated men and stopped in believing in god due to her father leaving her, and never coming back, despite of countless prayers she sent. In result, she had turned into a nagging, unhappy girl. With the help of a frivolous childhood friend that seems to see through her, can she move on and smile again?