The quest "The Return of the Fallen Gods" is available from level 14 and can be obtained from the Forest and Lake hermits on the Isles of Swirling Mist. They will send you to the ancient altars on the Daigon Islands and Scolopendra Coast.
The Spirit from the Shaat-has Altar will teach you how to kill the desecrated monsters and shatter the Shiass Shard of them. The first time you killed the Daigon Armakhton , you get a Shiass Shard. The spirit will tell you how to destroy the shards to increase your reputation as a Fighter against Shiass.
For each killing of the Scolopendra Essvesh , who lives in the Dancing Shadows Cave, you get the Tiny Shiass Fragment provided you have studied the Second Shiass Thesaurus.
For any further defeat of these monsters, you will continue to receive Shiass Shards, to increase your reputation as a Fighter against Shiass.