Love Alarm is an app that tells you if someone within a 10-meter radius has a crush on you. It quickly becomes a social phenomenon. While everyone talks about it and uses it to test their love and popularity, Jojo is one of the few people who have yet to download the app. However, she soon faces a love triangle situation between Sun-oh whom she starts to have feelings for, and Hye-young, who has had a huge crush on her.

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.