Authentication

Prior to the events of Mandatory, Curiosity disappeared for over a generation of litters a number of times to recover from any nasty injuries he received in a battles. Upon any return, he starts judging the living inhabitants of Media again, except now based on their older relative's actions. Some he's judged unfairly, and learned to give the benefit of the doubt, others he's found carried on their ancestors' bad habits.
Curiosity lost track of Solitude's bloodline, as the titles relating to emotions and actions, (Curiosity, Satisfaction, Conscience, Wisdom, etc.) was removed from Media long ago.  However, finding this new opponent brings it right back; Authentication's actions mirror their ancestor's past actions so much, Curiosity struggles staying in the present, stuck remembering the battles with Solitude clearly just upon sight of Authentication. Unsure if it's his own mind, the after-effects that Solitude's magic still may have on him, or the lingering fear that Solitude's magic might have passed down to his decedent, Curiosity's determined to end it once and for all. 
But Authentication's not one to back down in a fight.
(Source)