3.583 out of 5 from 26 votes
Nana is twenty four years old and has lived most of her life without any purpose. She is known to her coworkers to be indifferent and refuses to pay attention to others when they speak to her, leaving her with very few friends. However, Nana's life is turned upside-down when a car accident sends her back to her past; she awakens to find that she is now a fourteen-year-old junior high school student. As she relives her junior high school days, she slowly begins to uncover the painful memories that she had tried to repress as an adult. Will Nana's past help her find a reason to live or will it prove to be much more than she can handle?
On the way home from a business trip, 48-year-old Hiroshi Nakahara boards the wrong train and finds himself in the town of his youth. After visiting his mother’s grave, Hiroshi is transported back in time to his fourteen-year-old self – a time when his family was strong and his father hadn’t abandoned them yet. At first he’s thrilled, but soon comes to realize that he isn’t able to return to his wife and children, and must continue living in the past. However, Hiroshi is now left with a life-changing decision – should be try to change the past, without knowing what it will do to his future?
Both these manga are about adults whose lives are unfulfilling or incomplete in some way, that are suddenly transported back to their junior high days.
Both are about people time travelling to the past unexpectedly. In Harukana Machi-E, Hiroshi feels disconnected from his family, whilst in Heptagon, Nana feels like she has nothing of worth in her life.
Satomi's entire high school is assembled in the auditorium for the announcement: her old math teacher has been murdered. The news causes her classmates to burst into tears, but the girl remains stoic, even in the face of the rude sheep that she hallucinates. But her apathy doesn't stop her from getting sucked into the case: she becomes acquainted with Yukinari, who the police believe is involved with the murder. This man reminds Satomi of a boy in bloodstained clothing that saved her life ten years ago, when the apartment building that she lived in exploded under mysterious circumstances. And though that case remains unsolved, as time goes on more and more threads are discovered connecting it to the recent murder; just how are these two cases related?