The protagonist travels/is reborn into a different world where the financial system is extremely developed and extraordinary power is closely linked to capital. Here, "credit" is a resource that can be quantified, cultivated, and even directly converted into combat effectiveness (called "credibility" or "capital flow"). The more debt you owe, if your credit rating does not collapse, you can use huge debt leverage to leverage stronger "credibility." However, once your credit collapses, you will be counterattacked by the financial laws of the entire world, and you will die. The protagonist has obtained the "[Negative] System". The more debts he owes, the stronger he becomes, and the system can forcibly maintain his apparent credit rating.
