Having overcome the ferocious battle with the fearsome White Whale, Subaru Natsuki returns to the Mathers domain. With the subjugation force that overcame the deadly combat, and the addition of Julius, their common history reconciled, together they clash with the Witch Cultists under the command of Bishop of the Deadly Sins, Petelgeuse Romanee-Conti.
To thwart the vile schemes of "Sloth" aimed at Emilia and the others, avoid the tragedy he has witnessed multiple times, and to defy Fate itself, Subaru's "Return by Death" experiences open the way forward-! "So, let me ask this of you. -Let me cling to your back, while you carry me on it."