It didn't look like rusty iron.
This guide explores what CPK files are and the best tools available for editing them. What is a CPK File? cpk file editor
A is a utility designed to open, extract, and modify .cpk files, which are proprietary archive formats primarily used by CRIWARE in video games (like Pro Evolution Soccer , Danganronpa , and various Sega titles). These tools allow users to access compressed game assets for modding, such as textures, models, and audio. Popular CPK Editing Tools It didn't look like rusty iron
SUCCESS: File injected. New archive size: 4.02 GB. and modify .cpk files
Instead, here is a (not a paywalled paper) that many researchers cite: