Dragon Quest XI oneshot prequel by Hiro Mashima.

Hearing the rumor of a precious "flaming ice sword", Erik and his fellow apprentice thief Derek explore a snowy region in search of loot when they are caught in a blizzard and find themselves in Thief Cage, a village of thieves trapped by the curse of the sword in question. Erik, impressing the other brigands by his skill, decides to lift the mystery weighing on Thief Cage in order to find a way to escape from it.