[Sister-in-law + kung fu + invincibility + pretending to be a pig and eating the tiger]
In order to repay his kindness, he hid his identity as the God of War and was willing to become the son-in-law who stepped in, but he didn't want his beloved wife to be bullied. After that, he vowed to trample everyone under his feet so that no one in the world would dare to bully you again!
