This is the one I was least looking forward to, since the relationship with Soushiki is already pretty well defined, and there didn't seem to be much left to explore. In fact, there wasn't! Hitoshiki spends the entire book mistaken for Soushiki by the Betrayal Union, a group that consists of one member from each of the cursing families. A couple of the cursing families have briefly played roles before, but this is the first time the spotlight has ever really focused on them. We get a decent look at five of the families, but Toganari Togari gets killed offscreen without ever showing up, and Tokinomiya Shigure goes down surprisingly easily, so both of those families are still more or less a complete mystery.
Over the rest of the volume we have Hitoshiki engaged in a series of very Jojotastic battles with the Kino, Tsumiguchi, Nukumori and Shibuki representatives; each of them has strange powers, and is defeated once Hitoshiki works out what the power is and uses his brain to flip the situation. Or just wins by sheer luck.
While the epilogue does briefly wrap up a thread about Soushiki and Hagihara Shiogi, as a whole the book is pretty insubstantial; I love the Jojo formula, but it doesn't really make for the deepest of reads.