This anime is for mature audiences only. It is raw, crude, dark and a little depressing. It is a psychological anime meant to be an eye opener of how betrayal can lead to so much pain for so many people.
Kotonoha Katsura is one of the two main heroines (or villainesses) of School Days, she starts out as Makoto Ito's girlfriend after Sekai Saionji got them together. She also appears in the Summer Days and Cross Days as a secondary but important character.