The primary file is a decrypted CIA of the game Pokémon Sun . The "Region Free" tag indicates it has been modified to run on any 3DS console regardless of its original manufacturing region (Japan, North America, Europe, etc.).
Based on the filename and common distribution patterns in the homebrew community, Core Contents Sunv1RegionFreeCIA-ducumon.rar
The file extension for CTR Importable Archives, used with tools like FBI on a modded 3DS. The primary file is a decrypted CIA of the game Pokémon Sun
Likely the handle or "releaser" tag of the individual or group who uploaded or packed the file. Important Note Sunv1RegionFreeCIA-ducumon.rar