For high school students like Shouichi Kamita, university entrance exams and the future are common concerns. It is also during this time in life that a mysterious emotion that vexes people of all ages may begin to weigh upon one's mind—love. At this point in his teenage years, Shouichi finds three girls he could see himself having a future with: the ever-cheerful Hikari Tsuneki, who teases Shouichi without mercy, but actually has a softer side; the competitive gamer, Tooru Miyamae, who has difficulty communicating with others; and Shouichi's childhood friend, Kyouko Touno, the sometimes immature shoujo manga enthusiast. Seiren follows Shouichi's relationships with these three girls across three separate arcs, as their feelings grow from mutual interest and blossom into something more beautiful.

Facing goodbyes and graduation, Naomi Nakashima, her childhood friend Satoshi Mochida, and their classmates, are clearing up after their last ever cultural festival, when horror buff class representative Ayumi Shinozaki decides to perform Sachiko Ever After so they will stay friends forever. Instead, they were whisked away to a haunted graduation ceremony for Heavenly Host Elementary School, forced to close after a series of gruesome murders. What fate awaits Naomi and her friends at the cursed school...?

To bring back her dead friends, high school student Naomi (Rina Ikoma) goes back to the elementary school where a tragedy took place. She becomes involved in a new incident.