Kishou Arima is a famed Special Class Ghoul Investigator known as the CCG’s Reaper. He is undefeated as a Ghoul Investigator and at some point was formerly partnered with Take Hirako.
His investigative skills and prowess in combat has led many investigators such as Koutarou Amon to admire him.
He later passes down his Yukimura 1⁄3 (Koukaku) quinque to Sasaki Haise, a rank 1 investigator and mentor of Quinx squad. Along with Akira Mado, he is the overseer of the Quinx squad and keeps a check on Sasaki Haise along with the Quinx members.
During the third Cochlea raid, he begins fighting Sasaki, who has regained his memories.
Though Sasaki declared the battle over, Arima charged him and stated the battle will not end until one of them died. He continued to attack with the broken quinque, slashing apart tentacles until he closed the distance between them and stabbed Sasaki through his abdomen. However, Sasaki pleaded with him to accept his defeat, voicing his belief that continuing is meaningless. Arima stepped back, lowering his broken quinque and asked whether Sasaki has no intention of killing him. He turned his gaze upwards, musing that in his eighteen years as an Investigator, he has never faced an opponent he could not defeat. Once more, he asked Sasaki whether he will really not finish him off. Sasaki confirmed his decision once more, and after stating his understanding, Arima slashed his own throat with Owl.
Mortally wounded, Arima collapsed with blood pouring from his throat and mouth. As Sasaki held him, he used the last of his strength to confess his many secrets. He revealed himself to be a Half-human, a ghoul-human hybrid born without a kagune and bred by the Sunlit Garden. Because of his hybrid nature, he had developed glaucoma as a result of an accelerated aging progress and would soon die from old age. He revealed to Sasaki that the Washuu Clan are ghouls, and entrusted him with his final wish – asking Sasaki to take credit for his death. He promised that Sasaki would understand soon enough, and admited that he always hated his own existence as someone that could only kill, taking the lives of others while never giving anything to the world in return. With his dying breath, Arima praised Sasaki as something he could leave behind and lifted his hand to touch his face, before succumbing to his wounds.