I'd Like for Us to Be Friends.
It becomes apparent to Yuki why Kaori is losing her memory so he decides it best to keep his distance from her in order to preserve her memory.
Aired 23/06/2014EP 12 - I'd Like for Us to Be Friends.

2014
One Week Friends
The story revolves around Yuki, a boy who wants to become friends with his classmate and desk neighbor Kaori. However, she gently declines his friendship, saying, “But, my... Memories of my friends disappear in a week...” Even so, Yuki wants to become her friend, and so the two become friends over and over again as the weeks pass.