: Some utility programs like FileViewPro claim to open various obscure file types, though results may vary based on the internal data structure.

: In the context of 3D animation, a .vac file can store settings for accessories like clothing or specific colors used in the MikuMikuDance software.

Based on technical documentation, appears to be a specific instance of a .vac file, a format with several distinct uses depending on the associated software. Common Uses of the .vac File Extension

VAC File Extension: What Is It & How To Open It? - Solvusoft

Because .vac files are not a standard universal format, opening them usually requires the original software that created them. If you cannot access the original software, you might try: