"Weaponized karma" was a concept the deducers were all familiar with.
Some instance worlds placed great emphasis on cause and effect. People's choices determined what happened in the future. If someone's personal choice caused harm to another and led to a bad "result," that created karmic debt.
Those burdened by karmic debt found everything going wrong. They were restless and suffered greatly, their bodies wracked with pain as they waited for the day retribution came and they received punishment to match their debt.
Too much karmic debt could even affect reincarnation. If you died without paying it off, you would suffer the consequences in your next life, and the one after that.
There were many ways to deal with karmic debt, but aside from "offsetting it with good deeds" or "toughing it out," most methods involved varying degrees of malice. For example, exchanging fates with someone else and making them bear your debt, or using curses, borrowing someone's life, and so on...
These mystical methods could deceive "Heaven" and prevent new karmic debt from accumulating, then transfer the existing debt from yourself to someone else. In effect, you saved yourself by harming another.
The more instance worlds the deducers experienced, the more likely they were to encounter one with a system of karmic debt. Or, whenever a world involved cause and effect, there would be some concept similar to "karmic debt." The only difference was whether the term itself was explicitly mentioned.
Who would have thought that the people of Fengtou Town had such a clear understanding of karmic debt? They could even...
Stuff their own karmic debt into someone else's body, using it as a vessel to replace a soul!
They'd seen plenty of vicious things, but never anything this vile. This method eased the user's own karmic debt