Yoru was once a monk of Shidono Temple. After being killed by Nyx, he became undead via the magic of the Shadowfell. He was then banished there.
He was a monk at Shidono Temple. In 3E446, he took in a dying man into the temple. The man, paranoid, revealed himself to be a changeling named Nyx and killed Yoru and took his place. Taking on the name Yoruu and staying at Shidono Temple for a time, Monk Kazeshi saw through his facade but still gave him a chance.
The real Yoru meanwhile had been corrupted by the Shadowfell and disappeared from his unmarked grave, becoming an undead shadow. He fought the crew of the Phoenix Nebula in 3E452 on Cinohshima, and was banished to the Shadowfell once again after some captivity in Shidono Temple.