"Irises" are unique abilities most people are said to possess from birth. These powers manifest themselves in the form of visual cues and range from lie detection to danger prediction. Unfortunately, high school student Tooru Mizushima is one of the very few without an Iris. As an "Iris Zero," he is frequently bullied, and therefore, he tries to stand out as little as possible.

However, when the popular schoolgirl Koyuki Sasamori comes crashing into Tooru's life, his motto of minimal exposure is brutally shattered. Koyuki's Iris allows her to identify the most qualified person for a certain task—and she determines Tooru to be the most capable person to help her find the next student council president.

Tooru refuses to become involved in such a public affair, but Koyuki's cheerful persistence ultimately prevails. And so, Tooru's lonely life as an Iris Zero slowly changes as he comes to meet more people and utilize his exceptional deduction skills to solve various mysteries.