I know this might look obvious but the wording on this spell was a bit conflicting before the change in the SE rules :
Purge the Unclean Fire Battle: Bow this Shugenja, or bow this Spell if attached to a Fire Shugenja: Destroy one or more target attachments opposing this card up to the number of different Element keywords on cards in this Shugenja's army.
It says "one or more" and at the same time "up to the number of Element keywords in this army".
What is the procedure if the caster has no Element Keywords and the spell loses the Fire keyword and the Shugenja is alone in an army?
EDITED FOR CORRECTNESS