From Shadow Era Wiki

Steadfast is a keyword ability in Shadow Era.

Steadfast was introduced in Dark Prophecies. Steadfast causes any ally with this ability to not be able to be removed from the field by any method other than killing it. In other words, any cards that would return the ally to the hand (such as Retreat!) or cards that would exile allies (such as Loest, Savior of Layar) will not affect allies with Steadfast.