Ronin: Lone Warrior reads "While Ronin is active, once per turn, you may KO a Ronin die you control to prevent all damage from one source to you or a character die you control."
Polaris: Mistress of Magnetism reads "While Polaris is active, when one of your character dice is KO'd, you may pay [shield]. If you do, return it to the Field Zone at level 1."
I have 1 Ronin and 1 Polaris in my field. My opponent has declared attackers, I have declared blockers. Before combat damage is dealt, I KO Ronin to prevent the damage that will be dealt by an unblocked attacking die. If I use Polaris' ability to return Ronin to the field, can I use Ronin's ability again to prevent damage from another source? Does returning to the field reset the "once per turn" limitation of Ronin's ability?