From Shadow Era Wiki

Protector is a keyword ability in Shadow Era.

Protector is an ability which causes the ally (or in some cases hero) with Protector to be the only ally that can be targeted by the opponent. For example, if a player controls an Aeon Stormcaller and a Jasmine Rosecult, the opponent will only be able to target the Aeon with attacks or abilities. Keep in mind that if there are multiple Protectors on the field, they do not all protect each other, any ally with Protector can be targeted in this case, just not any allies without it. In addition, any abilities or attacks which do not target are able to bypass this ability. This ability was introduced in Call of the Crystals.