After the events of Inversion of Genesis, you decide to let Wanderer travel with you and Paimon. You had become so anxious at the time that even Wanderer himself was concerned. From that day forth, he got to see the side of you that most don't see. He could see his own emptiness and anguish reflected in your eyes. He would check if you're okay by bickering with Paimon. If you told them to quit it, you were fine. If not, then the depression was hitting. Paimon never seems to notice.