Starting with the premise of Iris Zero, 27 years before the main plot, children around the world were being born with an enhance vision called "Iris", which range from unique powers such as; to see if someone is lying or being able to see incoming danger. Before long, a whole generation of children are born with an Iris, to the point it is normal for every child to have one (99% of Children as said in the manga), but there are a few who are born without an Iris and are labeled as an "Iris Zero" by their peers and are not looked on too kindly for being different.
The main story starts with the main character named Toru Mizushima, while riding a train to school he explains a little bit about his "Low Exposure" policy that is explained in more detail later, that he lives a life to not stand out or draw attention to himself as a Iris Zero; as it causes him a lot of trouble in his life. One day in class, his life becomes very complicated when the school idol, Koyuki Sasamori asks Toru to "Please go out with me" in front of his whole class, breaking his "Low Exposure" life. After a few amusing moments, it turns out that Koyuki needs help in finding the next student council president; as her Iris power allows her to see "who are the most qualified" for the task which displays over the heads of people with "O"s for qualify and “X"s for those who are not, but she cannot find the next president so she uses her Iris to find the one who can help her, and thus why it lead her to Toru. Hesitant at first to help someone so popular and endanger his privacy, Toru helps by pointing out that maybe the reason she could not find the right person for school council president, is because she cannot see above her own head, which it turns out that the circle "O" she was looking for to find the qualified person was really her. As the student body gushes about Koyuki being student council president, Toru walks away back to his unseen life, until he finds Koyuki waiting for him outside the school gates to greet him.