Masayuki Muroi is a tall young man with a tough exterior, light skin, black hair, and black eyes. Despite enduring betrayals by his closest relationships—his best friend, colleagues, and ex-wife—which eroded his faith in humanity and drove him toward isolation, he exhibits extraordinary kindness devoid of revenge or malice. This persistent benevolence frequently perplexes others.

His pivotal experience unfolded when his best friend Hayato pushed him from a snow mountain and abandoned him to die. During the near-fatal fall, the supernatural Yuki-Onna manifested. She first teased about killing him but, struck by his physical appeal, rescued him instead. In exchange, she seized half his money and imposed a death-bound secrecy pact: revealing their encounter would cost his life. Masayuki accepted her terms.

After surviving, Masayuki returned to the mountain cabin where Hayato had falsely declared him dead to authorities. Masayuki refuted this, claiming he found a path down the mountain, and reported Hayato’s murder attempt, resulting in Hayato’s arrest.

Masayuki later reunited with Yuki-Onna and allowed her to live with him. He freely spent his money on food and cooked for her, displaying unwavering kindness despite his disillusionment. Their bond evolved into mutual romantic affection, and Yuki-Onna became his live-in girlfriend. Masayuki’s trust in her remained absolute, even as others questioned his openness given his past. Yuki-Onna perceived him as exceptionally kind and reciprocated with profound trust.

While interacting with other supernatural beings like Hanbei Hakusho and Mataemon Masakatsu Inoue, Masayuki maintained skepticism toward human connections outside his relationship with Yuki-Onna. His development centers on transitioning from isolation to a devoted bond with her, underscoring his capacity for forgiveness and absence of bitterness despite trauma.