Touma and Kento depart to look for the mythical land of Avalon so the former can unseal his sword, but Calibur stands in their way, intending to claim the secret power located there for himself.

After his recent feats, Touma is recognized by the others as a full-fledged member of the Sword of Logos, but when the Megids prepare multiple Alter Books for their next plan, Tetsuo Daishinji, the order's mechanic, joins the fray as Kamen Rider Slash after repairing his own weapon.