All the events that happened so far involving Pater-Mater.
Trails in the Sky SC
Trails in the Sky the 3rd
Zero no Kiseki
Pater-Mater remained stationed in the Rosenberg Studio's basement under maintenance. It first appeared before the Special Support Section and Yin after liberating the St. Ursula Medical College from the controlled-mafia's occupation. After jetting off with Renne, tt presence left them stunned and speechless witnessing it for the first time.
It reappeared to save the SSS, Estelle and Joshua from their restrained grasp by a demonized Joachim. Using it Double Buster Cannons, it destroyed the tentacles freeing them while also weakening Joachim and the party used all their Crafts until he eventually disappeared. Just before Pater-Mater can fly Renne off, it halted for Renne to listen to Estelle and Joshua's full understanding of her background and how they still wanted to be her new home. Through the Meister's adjustments to its AI, it let her down to the siblings despite Renne commanding not to. Unseen since, it presumably followed Renne back to Liberl.