I'm still really interested in this.

I have an idea: what if the Protectors were worshipped by ancient peoples, thousands of years before the fall of the Protectors to mortality? Temples were built in their honor, holding purifying and powerful waters with their blessing. These waters would simply act on a normal man with whatever effect the Protector gave, but on mortal Protectors, these waters would reopen their powers. But over time, as men forgot their Protectors, the temples fell into ruin. The temples were lost to time and forgotten by all mortals, locations unknown. When the Protectors fell, so too did they forget their temples. Some temples fell into the ocean, some temples were buried by dirt and sands, some temples were overgrown with nature, but for each temple the same happened: each would fade from all memory and each would succumb to the elements and disappear. Even still within the temples of the Protectors were sanctuaries hidden behind what seemed to be their final chambers wherein the water was. In these sanctuaries, there was a door of sorts. Not a physical door, but a great seal on the floor with intricate patterns and runes. These seals were connected to the realm from which the Protectors hailed. When fate allowed and the mortal Protectors had enough power and came to understand their roles fully, their sanctuaries would open to them, and their full potential would be unlocked as the seals broke and the powers surged into the Protectors.

Of course, for balance's sake, the Protectors would have to go through trials and battles with monsters and the like to get to their temples and to harness their powers from their temples, but the idea is the same. The temples are a way for them to restore their power because they still hold the subdued energy of the ancient people who believed in them. Perhaps the temples were even built on top of by some people, like a temple could be hidden somewhere within a king's castle or a palace, or underneath a new religion's main place of worship or center of power.

(Feel free to take this idea or modify it however you wish, but I thought this would be cool to suggest.)