Retribution for Sin Sources

Retribution for Sin (often referred to as a horn) is the rare material used for enlightening units for the last step in Gluttony Gate and Wrath Gate. This material is in limited supply to free players but is sometimes available from enlightenment summons as step rewards or for gems or from bundles. Note that there are also Otherworldly Retribution which are used to enlighten collaboration units from other worlds (i.e. not the ones that are alternate versions of our normal units), but they are more plentiful and are usually obtained from collaboration events.

Event Acquired
Most free Retribution for Sin are obtained through events, some of which will run periodically or are permanent, and some of which are only expected to run once. We aren't generally informed which events will rerun again later.