A young man who met Akagi in the short time he worked at the toy factory. Though small and usually nervous, as well as oblivious to cheating around him, Osamu is a good mahjong player if the stakes are low.

While mahjong is a game that is often played with family and friends, it is also a game that is played in the darkest corners of society. Nangou is a compulsive gambler who has accumulated a debt of over three million yen. In a last-ditch attempt to clear his record, he decides to wager his life on a game of mahjong with the mafia. Unfortunately, as the game progresses, Nangou only moves further from the prize and closer to death.
 
When all hope seems lost, the game parlor is suddenly intruded upon by Shigeru Akagi, a young boy on the run from the police. Desperate to turn the game around, Nangou hands the game over to Akagi after teaching him a few of the rules. The mafia can only smirk as Akagi sits down to play. However, they soon come to learn that Akagi is a natural-born gambler. An imposing figure who does not fear death. One who is destined to become a legend.
 
(Source: MAL Rewrite)

While mahjong is a game that is often played with family and friends, it is also a game that is played in the darkest corners of society. Nangou is a compulsive gambler who has accumulated debt over three million yen. In a last ditch attempt to clear his record, he decides to wager his life on a game of mahjong with the mafia. Unfortunately, as the game progresses, Nangou only moves further from the prize and closer to death. 
When all hope seems lost, the game parlor is suddenly intruded upon by Shigeru Akagi, a young boy on the run from the police. Desperate to turn the game around, Nangou hands the game over to Akagi after teaching him a few of the rules. The mafia can only smirk as Akagi sits down to play. However, they soon come to learn that Akagi is a natural born gambler. An imposing figure who does not fear death. One who is destined to become a legend.

Japan has entered a new era called "Reiwa", after moving past the Heisei Era on April 30th 2019.
 
It is in this era, past the time of people like the legendary Akagi Shigeru and others like him who gambled on mahjong for a living, that a new gambler has arisen known only as "Mamiya of Mahjong's Darkness".
 
(Source: Original publisher, edited)
 
Note: The chapter counts contains "Chapter 0".

Osamu Nozaki