- Entity or sentience attached the system created by 'The Path' to act as an intermediary and guide for Vahn Mason. She seems to be evolving slowly over time to accommodate Vahn's mental state and desire for kinship.
- Though she would willingly change to reflect any form Vahn had decided for her, Sis kept it a secret that she 'already' had a body. She would never allow him to try and separate them, as there was no form of intimacy closer than what they currently shared, but, knowing he would eventually want to meet her, she had conceived the closest thing to an ideal big sister that existed within Vahn's mind. This image had changed with the passage of time, but, while her figure had been modified quite a bit, there were a few things that had persisted since Vahn's time in Danmachi.
- As she was his 'big sister', Sis had healthy brown skin that was similar to Vahn's. Due to the early influence of people like Milan, Tina, and Choe, however, her default appearance was that of a Cat Person. She had short hair that was like a fusion between Vahn's and Chloe's, but, unlike the vast majority of Cat People, her figure was anything but lithe. She was very petite, only standing around 158cm tall, but, similar to Arnya, she had an uncharacteristically voluptuous body. Her breast could easily contend against the bustier women in Vahn's entourage while her tail, despite appearing like a traditional Cat Person's, was inordinately thick and fluffy.