Lacking in self-esteem and suffering from social anxiety, eighth-grader Hikage Sumino has remained unnoticed throughout her life. Upon entering middle school, she made a personal resolution to make some friends, but even at the end of her first year, she remains fruitless. Her only comforts are a lonely flower she found and regularly cares for, and "1 Centimeter of Happiness," her sunflower-themed internet blog where she regularly posts her thoughts and experiences. Though she usually gets only two visitors on her blog, Hikage finds satisfaction in their comments and appreciates their support.

One day, she is surprised to find out that two of the most popular boys of her school, Hinata Mutou and Teru Mikami, are aware of her presence and remember her name. Dazed by this sudden revelation, she posts about this encounter on her blog and gets an inspiring comment from one of her regular visitors. Taking her internet friend's advice, she gains some confidence and aspires to change her world for the better.