Miyu is a cousin of Nagayama Amaya (now Saito Amaya due to marriage to Saito Jon). They were not raised together, and did not know of each others' existence for many years, as Miyu grew up in a monastery in the mountains. But the Kemonoken style that Amaya created was eventually taught to her when they met on one of Amaya's missions away from the Village, and Miyu has been working to improve her mastery of it ever since, while having her own adventures and engaging in her own battles and studies. She has divided her time between education, research, supporting the temple, and her training, leaving her far behind where Amaya was at the same age.
Miyu never took any vow of celibacy, and has had partners over the years, though long-term relationships never seem to work out due to her insistence on duty going before any degree of personal connection. The latest, the father of her daughter, was a shinobi of the Hidden Leaf who received medical care at the monastery and had a brief if intense relationship with Miyu. But when he received the same degree of distance, where she cared for him as an ally and a friend, rather than as a lover or the father of their child, he made his way back to Konoha.
However, he never made it back, ambushed by the Storm Brigade. Miyu received word, and showing an uncharacteristically emotional response, tried to find him and his ambushers herself. She arrived in time to hear his dying words, pleading with her to use the Eight Gates that he had tried to teach her in order to defeat the Storm Brigade, and obtain vengeance for him. In those last moments, there was a hint of the bond that should have been there from the start. The love that should have been the foundation of their relationship as parents of their daughter. But then he was gone. And that dream of a change to Miyu's outlook died with him.
Miyu not in top-shape thanks to recently giving birth, received an injury to her right eye in the course of battle. She was unable to track down the members of the Storm Brigade who had personally attacked her lover, and had no intention of seeking something as hateful as vengeance. But she did wish to bring them to justice.
Now that the Storm Brigade have made war against the shinobi world, Miyu has aligned the Fierce Beast School with the Village of her cousin, in the hopes of joining forces to end the conflict before it can spread any further. She was made Kemonoken Fierce Beast Grand Master due to her wisdom, leadership, knowledge, and strength, not just her skills, but her decision to take up a military affiliation with one of the Villages has made some of those who didn't support her in the first place to have even more doubts, and start to work against her.
