From Johou Battle:

A Great Magician and the head priestess of the Myouren Temple. She was once a human priestess spreading buddhism and protecting humans from yokai, but this changed after her brother Myouren's death. In her grief, she began practicing magic that would preserve her youth. At some point she realized that she'd not only need to protect yokai to protect her magic, but yokai were worth protecting in their own right, which Byakuren's wisdom, magic, and strength can do with ease! Byakuren is humble, infinitely patient, and disciplined, even refusing to partake in the vices of eating meat and drinking alcohol.

Byakuren works admirably every day to promote peace and equality between humans and yokai across Gensokyo in any way she can!