Oh, is Byakuren talking about Myouren? Did she meet him here?
The Shigisan Engi, the picture scroll the historical Myouren's story is mostly known through, features a story where the monk Myouren's elder sister walks across the country to find him after not seeing him for 20 years (guided by a purple cloud). I.e. the very story Byakuren is (very loosely) based on is about their reunion, but one that took place before he died and she became a youkai.
