As he witnessed his father's suicide as a young child, for which his father wrote a note to "those who betrayed him" on his business and social ventures, Mamoru grew to despise those who were betrayed, believing them a cancer to society and worthy of suicide. He expounds on this belief to Rika and anyone who will listen, with his doctrine explained thusly: those who earn betrayal earn death. From this he has a great fear of betrayal, going to great lengths to avoid it;
he ends up breaking the rules of the organ, for which he is killed by the Administrator.
While dying, he releases Rika completely from his brainwashing, but leaves his Apostle abilities. Though originally seen as an act of kindness, the Adminstrator teases out the truth: Mamoru's legacy would be concreted if even one person realized his doctrine of their own free will. He dies defiant of the organ and sure of his doctrine.
