C668 Children's Daughter-in-law
As for why he chose to become a disciple of Guanyin instead of a rogue cultivator, it was because he was afraid that he would bear too much merit and would be killed by the Heavenly Dao. Buddhism was, to a certain extent, a great sect recognized by the Heavenly Dao in this era!
That was why Mu Zha chose to sit in Guanyin. However, there were pros and cons to this