Loner Life in Another World Novel Volume 12 was written by Shoji Goji with illustrations by Saku Enomaru.

The infiltration of the Grand Cathedral begins! Motormouthed high-school loner Haruka launches his assault on the Theocracy's evil pope. Inside, he fights off swarms of fierce enemies to discover a sealed treasure chest, and inside—the body of a long-lost friend of Dungeon Emperor Nefertiri.

Haruka embarks on a quest through the Grand Cathedral to find a way to bring the beautiful girl back from the dead. If he succeeds, he'll face his most powerful enemy yet!