Originally, this anime was from the manga series (which in most cases, a lot of anime comes from manga) by Matcha Hazuki.
Synopsis: It all takes place in high school. There's one guy named Yuki Hase. He's very interested in Kaori Fujimiya. He wants to be friends with her. Hase isn't really a smart kid. Fujimiya, however, is a smart girl (especially math) who chose not to make any friends because she forgets memories that related to her friends every Monday. Hase then tries to be friends with her. Will he be able to open Fujimiya's heart to make friends and memories? Find out by watching :)