Using a Hex Editor (like HxD), the first few bytes will confirm if it is a true 7z archive (look for the header 37 7A BC AF 27 1C ).
This prefix is frequently associated with Studio S or specific Japanese digital asset creators (often related to "Violet" or "Vio" themed character models or animations). Likely Contents SS-Vio-003_v.7z.001
It uses the 7-Zip compression format, known for high compression ratios. You will need software like 7-Zip or WinRAR to open it. Using a Hex Editor (like HxD), the first
Often for use in software like MikuMikuDance (MMD), Unity, or Blender. Using a Hex Editor (like HxD)