This arc is centered on Yui. I thought she got very short shrift, canonically, and was handled illogically to boot. So these stories address the question: Why did it all happen that way, and what would happen after?

A Yamamoto/Gokudera arc in which Yamamoto decides Gokudera could really use someone to take care of him since he doesn't seem to attend to that at all himself.

The arc in which Tsuna tames Xanxus. Sort of mental Tsuna/Xanxus, not always in an amiable way.

Hibari's arc, moving through some of the events canon implies but does not show. Eventual Dino/Hibari.

101 ways to fix Xanxus. This series contains Alternate Histories all of which experiment with what changes might have led to Xanxus being only a little broken instead of totally insane.

This is a dark Alternate History arc that follows what might happen if Mukuro had decided to make Xanxus his tool of conquest instead of Tsuna.