Keyboard

Description
A Keyboard is something typically used for writing, but it can double as a deadly weapon on the right hands, it is 1000000% possible to kill someone employing them this way. It is well known that a true yakuza will only ever use a gamepad, so in this sense, using a keyboard would destroy his status and pride as yakuza, and thus only evil criminals and honorless yakuza dare to wield them as weapons. Thus, Keyboards became the conceptual antithesis of any real yakuza who carries himself with honor.

Season 0
In the past, there was an event centered about keyboards, where Kiryu Kazuma lost his sworn brother Matou Kariya by the trickery and manipulation of Sudou Tatsuzou.

After Kiryu returns to Coolsville, Sonozaki Steven is knocked out and falls ill after being attacked with one, and Kiryu & Kasai Tatsuyoshi react in disgust when they figure out there's a monster somewhere using keyboards against them.

Osama bin Laden then reveals the connection between the current events and the keyboards from years ago, and that they are being stockpiled in a Policial warehouse at Coolsville's Docks.