Mamoru Akasaka serves as a Tokyo Metropolitan Police Department Public Safety Division detective. In June 1978, he investigates the kidnapping of Toshiki Inugai, grandson of Japan's Minister of Construction, leading him to Hinamizawa village. There, he collaborates with Okinomiya detective Kuraudo Ooishi. Akasaka's pregnant wife, Yukie, is hospitalized in Tokyo during this time, causing him significant concern about missing her delivery. In Hinamizawa, young Rika Furude warns Akasaka to return to Tokyo immediately, predicting annual deaths and disappearances culminating in her own death in June 1983. Akasaka dismisses her warnings. Rika attempts to prevent him from learning about his wife's condition by cutting phone lines. Despite this, Akasaka later discovers Yukie died from a fall down hospital stairs shortly after giving birth to their daughter Miyuki. A subsequent janitor accident on the same stairs revealed the hazard; heeding Rika's warning could have prevented Yukie's death. This failure haunts Akasaka with years of guilt and regret. Raising Miyuki as a single parent, Akasaka immerses himself in karate training, developing into a formidable martial artist as both a coping mechanism and a reminder of his failures. By 1985, reunited with Ooishi in Sapporo, they discuss the Great Hinamizawa Disaster and Rika's accurate predictions, realizing she genuinely sought help years earlier. They co-author the book "Higurashi - When They Cry" documenting the tragedies. An alternate 1983 timeline (Minagoroshi fragment) shows Akasaka heeding Rika's initial warning. He returns to Tokyo, warns Yukie about the stairs, and prevents her death. Grateful, he vows to repay Rika and arrives in Hinamizawa during the Watanagashi Festival season. However, staying at a distant hot spring with Yukie causes him to miss critical events, leaving Rika disappointed. Akasaka's most significant involvement occurs decades later (Matsuribayashi fragment). Now a highly skilled karate master and investigator, he thwarts a diplomatic security leak and reflects on his failures. Through a metaphysical connection, his skills and memories transfer to his 1983 self in a new timeline. Recalling Rika's warning that saved Yukie, this version investigates corruption linked to the Irie Clinic. He contacts Ooishi, confirms Rika's predictions are unfolding, and returns to Hinamizawa to protect her. He reunites with Rika, who emotionally embraces him. Working with Ooishi, Irie Kyousuke, and Tomitake Jirou, Akasaka helps uncover Takano Miyo's plot. He stays at Rika's house for protection, develops coded communication with Irie, and learns about the Mountain Dogs paramilitary group. His karate expertise proves crucial when he single-handedly defeats a Yamainu squad led by his old rival Tetsurou Okonogi, encountered previously during the 1978 kidnapping. In later years, Akasaka revisits Hinamizawa's remains with colleagues like Sawada, discussing connections between the Great Disaster and Takano's research. In comedic manga adaptations, he appears at a festival with Yukie and Miyuki, where Rika calls him "father," causing Yukie to briefly suspect an affair before the misunderstanding resolves. Akasaka evolves from a somewhat naïve, duty-bound detective in 1978 to a resolute, skilled officer driven by justice. He maintains strong loyalty, evident in his devotion to Yukie and determination to protect Rika as atonement. His background includes youthful mahjong proficiency, abandoned after Yukie's disapproval. The trauma of loss shapes him into a staunch opponent of evil, with his karate prowess symbolizing enduring remorse and resolve.