Keiji Sakashita is an antagonist of the visual novel and later anime Grisaia no Kajitsu. Keiji was a member of a wealthy family, the father of one child, his daughter Chiaki. Keiji is known to be an avid hunter and, rarely among Japanese, actually owned a firearm, a shotgun.

Keiji was unhinged after his daughter Chiaki was killed in the aftermath of a bus crash in the wilderness. Unknown to Keiji, the survivors had been driven to insanity by food poisoning after Chiaki and their teacher, Yoshihiko Ochi, had tricked most of the students into resorting to cannibalism. Chiaki died of disease shortly afterward.

Keiji was infuriated by his daughter's death, and blamed the only survivor of the incident, Amane Suou. Keiji finally caught up with Amane years later, and initially introduced himself as "a fan" of hers. Yuuji Kazami, Amane's classmate, and unknown to either Amane or Keiji, a former child soldier who had enrolled in the school in an attempt to have a "normal life", however, was suspicious of Keiji.

Keiji goes to Mihama Academy, where Amane and Yuuji attend, and takes the other four girls at the school hostage. Yuuji and Amane return to find the place blockade by SWAT forces associated with the agency Yuuji is affiliated with. Amane bravely enters the building and lures Keiji into a bathroom where Yuuji can get a clear shot at him.

Keiji attempts to rape and then murder Amane, however, he is shot by Yuuji with a sniper rifle. The shot wounds Keiji, allowing Amane to disarm him and rescue her friends. Keiji is arrested shortly afterwards.