Is the game a or wrapped in an .exe installer? Do you have access to the System.json file?
An .rpgmvp file is an encrypted PNG image created by RPG Maker MV, an engine developed by Enterbrain (now a part of Kadokawa Corporation). When a developer deploys (exports) their final game, the RPG Maker engine automatically encrypts all its original .png image assets. This process produces files with the .rpgmvp extension to protect the game's visual resources from being easily accessed or modified by unauthorized users. Rpgmvp To Jpg Converter -UPD- Download