Sin Shell

A Sin Shell is a hardened black shell that sometimes forms supernaturally on the backs of those suffering from severe regret. The shell is heavy and cumbersome but it does provide some protection as well, and if it is large enough, its user can retreat inside of it completely. It grows in size with the regrets its user has, especially those of past sins. The burdens they carry in their mind become the burden they carry on their back.
Observers often note that those who wear the shell resemble snails, snails being crushed under the weight of their past. The spectators suggest that the users would be better off shirking those burdens if they can. Users of the shell, however, counter that then they would simply slugs and they doubt they would be any better off.