Algernon ni Hanataba o is based on the award winning work Flowers for Algernon by Daniel Keyes.Abandoned as a child by his mother, Hasumi Sachiyo (Ishida Ayumi), Fujishima Haru (Yusuke Santamaria) is a mentally challenged man that has grown up and worked at the Sakurai Bakery as a baker. Working with him at the bakery is the owner Sakurai Kyoko (Nakajima Tomoko) and Tashiro Miki (Enomoto Kanako), a girl who is also mentally challenged and is like a sister to Haru. At night, after the bakery is closed, Haru and Miki attend a night class with other mentally challenged adults. Their teacher at the class is Toya Erina (Kanno Miho) who not only is their teacher but also their friend.One day, Erina is approached by her old friend Kobayashi Rumiko (Ishibashi Kei) about a candidate in the research she is conducting with Professor Tatabe Shinichiro (Masuoka Toru) and Tokunaga Atsushi (Taguchi Hiromasa) that could possibly increase the intelligence of the mentally challenged. Reluctant at first, Erina changes her mind when she sees the resolve in Haru to become smarter so that his mother will come back for him.With the success of the surgery, Haru becomes more and more intelligent. However, with his newfound mental abilities comes problems. Haru now must face the challenges his new self-awareness presents such as the people around him and his own emotions.