Master Key

The Master Key (親鍵, Oyakagi) is a key shown to be used several times during the civilians' trip to Kongoukaku. It is a tool that enables the user to control the Koutetsujou and it's cars.

It was initially used by Ayame to manage the Koutetsujou, however, it was later used by The Six Chiefs after taking control of the locomotive. 主鑰匙