Eri
About
Eri is a mysterious middle school student, and also the only one who actually liked Yuuta's movie, though she points out its flaws as well. She meets Yuuta on the rooftop of the hospital where his mother passed, and prevents him from committing suicide by dragging him along with her and making him watch a lot of movies, announcing that she would help him craft a much better movie for next year's school festival.
She claims to "watch more movies than anyone in town", and helps Yuuta approach filmmaking from a more critical perspective. In his new movie, Eri ends up playing the part of a vampire girl who prevents Yuuta's suicide, whose life would end soon because of an illness.
Eri is also suffering from a terminal illness. She confesses to being envious of Yuuta's mother, whose live was partially recorded so that her memory could live on. Like her, Eri requests Yuuta to film her last moments.
After the second movie, Goodbye Eri, is concluded and Eri passes away, it is revealed that, unlike the character in the movie, the actual Eri had worn glasses and a dental retainer. Her and Yuuta had only acted as a couple for the movie, as she had rejected his real-life confession.
Of course, Eri's entire character as seen in the manga, is open to the reader's interpretation, regarding how much of her life is real and how much is part of a movie.