Complex sentence: Her origins are a mystery as she first materialized on Earth before Gengo Aoi and it is hinted that she was Kazuya and Kazuha's grandmother as well, which could explain the high concentration of Stigmata tissue into their bodies.
Split into simpler sentences: Her origins are a mystery as she first materialized on Earth before Gengo Aoi. It is hinted that she was Kazuya and Kazuha's grandmother as well, which could explain the high concentration of Stigmata tissue into their bodies.