The Supergirl: Candor arc had a story hinted at, but never done. It involved Power Girl fighting Saturn Queen and her henchmen in a war through time for the soul of Supergirl, or somesuch. PG, who seemed to be immune to SQ's powers, was said by SQ herself to have fought for SG, who SQ seemed to want for reasons other than simply marrying Ultraman. They never followed up on that, and I wish they would.