The Sun Wood Saber

It was because the academy discovered that there was a huge problem with him. It was his bloodthirstiness. 

When Yun Tianheng was young, his family met with misfortune which resulted in his change of temperament. He was an extremely introverted person, so on most days, he barely spoke. He did not have many friends, but he did not appear to be unusual when he was accepted into the academy. From the outside, he seemed to be a young man focusing all of his time and energy on cultivation. 

Eventually, he exposed his true nature in a sudden accident and was expelled by the academy. 

Yun Tianheng's cultivation base was already very high when he left Shrek Academy. However, Shrek confiscated his battle armor, so he ended up being just an ordinary soul master. Moreover, he also had to bear the dishonor of being expelled, so he was not welcome anywhere. 

He then plunged himself into the Spirit Pagoda. His fame was spread by word of mouth all over the continent.