Mamoru is the main character in Himatsubushihen. He is a young police investigator at the Metropolitan Police Department in Tokyo. He befriended Rika while investigating a case in Hinamizawa four years ago all due to a prophecy about his wife which came true though he just brushed it off as coincidence. In an untold world Mamoru regrets being unable to save his wife and Rika and learns martial arts to clear his mind hoping to relive the time before Himatsubushihen to save them. Through a miracle Mamoru inherits his martial art skills in Matsuribayashihen using them to singlehandedly defeat a Yamainu squad and decides to save Rika from her destined death as a payment for saving his wife through her prophecy.