Characters given the role of 'assist only' are non-playable characters that can only be used in assist attacks. This idea started in Dissidia 012 Duodecim with the character Aerith Gainsborough. Assist only Characters cannot have any role in storylines.
Assist only characters often are designed around characters that have low combat potential or lack proper combative abilities. Instead they often can grant unique characteristics such as granting immunities to their caller, using unusual or powerful attacks or preventing opponents from moving.