Take the five crests to Rubiss' shrine (located north of Osterfair by ship) to receive Rubiss' Charm. The echoing flute will help you locate the crests. If you still can't find them, look below.
Sail west of Zahan, to the fire shrine search in the upper right corner to find the crest.
Once you have all the keys, go to Hamlin and fight the demons to get the crest.
There is a tower South of Alefgard. Climb it, and follow the old man to the treasure chest. Surprise! He is a demon. Defeat him to get the crest.
Beat the tiger in Osterfair and the king will give you the crest.
Search the bottom floor of the cave to Rhone to find this crest.