Heptagon summary:

Nana, an apathetic 24-year-old with nothing much in her life, suffers a car accident and wakes up in her 14-year-old junior high body. As she lives through each day, she starts to remember things she buried deep in her memory, and she can now not remember being involved with her older sister, whom she deeply admires, and her sister's first love, a senior at her school.