The "RJ" prefix is a standard product identifier used on DLsite , a Japanese digital marketplace for independent games and media. Game Overview
The main file to run the RPG Maker-based game. Manual/Readme: Instructions on controls and gameplay. RJ373560.zip
While originally in Japanese, English fan translations (such as v1.0.0 ENG) are commonly distributed in archives with this filename. The "RJ" prefix is a standard product identifier