Yuuko Shinozuka

She has always longed to enter Nishi High School and Ayumu, not wanting to be apart from her friend, promised to study hard for the entrance exam. When the results came out, Ayumu passed but Shii-chan did not. Enraged, Shii-chan blamed Ayumu and said she never wanted to see her again.

That same night, Shii-chan attempted suicide, and Ayumu felt she was to blame. At Nishi Kou, Ayumu vowed never to make friends again so she will not have to hurt anyone anymore.

(Source: japinoy.vox.com)