When Castlevania: Harmony of Despair launched on the PlayStation 3 in 2010 (and later on Xbox 360), it broke the traditional Metroidvania mold. Instead of a sprawling, interconnected castle, Konami delivered a 2D action-platformer focused on 6-player online co-op, speed runs, and loot grinding. But the true longevity of the game didn't come from the base title—it came from the mountain of downloadable content.
The base game of Harmony of Despair is a 6/10. It is repetitive and shallow. The full game —with the DLC installed via PKG—is a 9/10. It is a chaotic, beautiful mess of grinding for Valmanway swords and Sonic Boots. Castlevania Harmony Of Despair Dlc Pkg
The Complete Legacy of Castlevania: Harmony of Despair DLC Packages When Castlevania: Harmony of Despair launched on the
When dealing with Castlevania: Harmony of Despair , PKG files are used to inject extra characters, stages, and music packs into the base game when using PS3 hardware or PC emulators like RPCS3. The Complete DLC Roadmap The base game of Harmony of Despair is a 6/10
It sounds like you're looking for a guide on installing or using in PKG format (typically for modded PS3 consoles or emulators like RPCS3).