There is one event after he leaves Three-Realms where he does something that grants him such huge amount of merits that it literally takes form around him, after that pretty much no bad karma can affect him. XD
It's only a spoiler of a side event, but click the spoiler button at your own risk because it's quite detailed. After he joins a country that is fairly powerful, he becomes one of the strongest genius there. 3 others and him win a competition to go on an adventure into another universe along with the disciple of the Overlord that rules the country. When they are adventuring, they get teleported into a space that have puppets that abducts anyone who enters, and tortures them etc, Ji Ning and the other 4 are ridicuously strong in their level, and naturally avoids capture, and when they investigate they discover millions of people incarcirated and being tortured/killed, along with that, there is a HUGE amount of resentment filling the air, as if the dead are still there hating them.Ji Ning and the other 4 are then discovered by the Divine Clone of the leader(The leader's true body is somewhere else) and they end up fighting. Ji Ning and the other 4 kills the leader, captures or destroys all the puppets and free the millions of caputured innocents. They end up recieving a HUGE amount of merit that it took the shape of glittering gas around them because they not only obtained the merit of the people that were captured, but by the ones who were killed as well, in a way of "bringing justice". So they got a huge bump in Karma.
After killing 10B innocent people and surviving his "karmic tribulation", will JN get a badass baleful aura? When JN met Northmont Blacktiger it was said that if you do many bad things you will get such an aura and iirc Blacktiger had such an aura and I don't think that he has the balls to do something equivalent to killing 10B people...