Masaaki Shimon

Masaaki Shimon, also known as Mon-chan was part of Kenji's circle of friends during his childhood. In 1969, he and his friends built their own secret base. They built this on a large field. He moved to Germany and became a rugby player before retiring to take care of his ailing mother. After her passing, he started his own business with a partner.

Spoiler

He returns to Japan to attend Donkey's funeral, and later answers Kenji's call to arms on Bloody New Year's Eve. Mon-chan survives the event, but prior to this, he was diagnosed with a terminal illness. He is later seen hospitalized in 2002 due to his disease.

Spoiler

In 2002, Mon-chan was already seriously ill and in the hospital. He was visited by Yukiji, to whom he showed the information he has collected while investigating the Friend. Shortly after, Mon-chan suddenly leaves the hospital with no warning and disappears, which is later revealed to have been to contact Sadakiyo in an attempt to investigate further, not knowing Sadakiyo's involvement with Friend. Sadakiyo kills him on behalf of the Friend, taking the information he has gathered.