To get DLC working for Castlevania: Harmony of Despair using .pkg files (typically for the PS3 emulator RPCS3), you must install both the DLC package and its corresponding .rap license file. Without the license file, the emulator cannot unlock the content, often resulting in "Demo" mode or missing characters.

Chapter 8: The One Who is Many: Based on Symphony of the Night, focusing on the Legion boss.

Pro tip for RPCS3: Use the "Dev Blink" patch to remove visual flickering. This is unrelated to DLC but improves the experience.

Conclusion

The .rap File: This is the digital license. Without this, the PS3 won't "unlock" the content you just installed.