This is addtional content that enables the following songs:

Banki-chan wa Mou Darenimo Tomerarenai
Tsukikake (feat. Coro)
Lamento (Dankagu Edit)
Rough Sea
Tenacity
Witches Rule (SIRIUS Remix)
Idoratrize World
HUNDRED DUOVIGINTILLION ARROWS feat. itori
Subliminal Seduction
The World Is Made in an Adorable Way

More details on the official game page of Extra Song Pack 6 ...