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.

Tsutsui Hikari (a.k.a "Tsuttsun") is a high school student who is content with his virtual life of anime and video games. One day, he gets stuck cleaning the pool with Iroha, a real live girl who is stylish, sassy and known to be easy with boys ... and she aggressively approaches him! Tsuttsun, who has few friends and lives in his own world, finds himself smitten by the confident and wild Iroha ... and his whole world is turned upside down!! It's the awkward and pure love story of a boy who experiences relationship for the first time.

> One day, a girl who loves me will suddenly appear before me. Middle school teacher Nobunaga has always been dreaming of such a gal game-like situation. However, the one who appeared before him was Kichou, a 14-year-old girl who proclaims herself as his wife. Appears to have arrived from the Sengoku era, she mistakes Nobunaga as Nobunaga Oda and urges him to conceive a child with her. Thus begins the age-difference love comedy between a gal game-loving teacher and a Sengoku era expert princess.

One day, high-school boy Yamada bumps into the beautiful girl Shiraishi on the stairs (literally), and their lips touch as they fall. When they regain their wits, they realize that they have swapped bodies. As time progresses, the two realize that this is not the only mysterious happening in the school.